Case No:1999/0327/3
 
IN THE SUPREME COURT OF JUDICATURE
COURT OF APPEAL (CIVIL DIVISION)
ON APPEAL FROM CHANCERY DIVISION
MR JUSTICE FERRIS
Royal Courts of Justice
Strand, London, WC2A 2LL
Date: 5th July 2000

B e f o r e :

LORD JUSTICE ALDOUS
LORD JUSTICE SEDLEY
and 
LORD JUSTICE MANCE

(1)  DAVINA WHEATLEY
(2)  BORTEC LIMITED 
(Claimants/Appellants)
AND

(1)  DRILLSAFE LIMITED
(2)  FORCE GROUP SERVICES PLC
(3)  NIGEL TIMOTHY FOSTER
(4)  GEORGE NIGEL ANTHONY FOSTER
(5)  MICHAEL CARTER
(6)  PETER DAVIES
(Defendants/Respondents)
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(Transcript of the Handed Down Judgment of
Smith Bernal Reporting Limited, 180 Fleet Street
London EC4A 2HD
Tel No: 0171 421 4040,  Fax No:  0171 831 8838
Official Shorthand Writers to the Court)
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Mark Vanhegan (instructed by Gordons for the Claimants/Appellants)
David Micklethwait and Michael Edenborough (instructed by The Law Partnership for the Defendants/Respondents)
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Judgment
As Approved by the Court
Crown Copyright ©

ALDOUS LJ:
1.  The appellants, Davina Wheatley and Bortec Limited, are respectively the proprietors and exclusive licensees of EP 0 689 488.  They appeal against the judgment and order of Ferris J of 23rd February 1999.  He found the patent invalid and ordered its revocation.  He also held that the alleged acts of infringement would not have infringed if the patent had been valid.  

2.  The first defendant, Drillsafe Ltd, was wound up on 29th April 1999 and was not represented on the appeal.  The other defendants supported the conclusions reached by the judge.  They also, in their respondents' notice, sought to uphold the finding of invalidity upon other grounds.  

The Patent
3.  The patent claims priority of 18th March 1996 and is entitled "Forming Threaded Holes".  As its title shows, the invention is of wide application, but it is said to be especially suitable for forming threaded holes in a tank, particularly in an underground tank for containing a flammable and volatile liquid such as petrol.  The specification describes the invention with reference to such tanks.  

4.  The specification describes how and why it may be necessary to form further openings in an underground tank.  Conventionally, the further opening may be formed only by removing the lid, drilling and tapping the new opening and then replacing the tank lid.  The problem is described in this way:
"In the case of a below-ground garage forecourt tank intended to hold petrol, the opening of the tank by removing the tank lid has to be performed with great caution and special measures have to be taken in order to avoid the risk of fire and explosion.  Generally speaking, this may be performed only once appropriate notice has been given to the local government authority.  The tank must be emptied of all petrol, and is then filled with water to displace all petrol fumes and vapours.  The above-lid pipe-work and other services have to be disconnected from the lid, and then the ring of bolts around the lid may be removed.  Once done the lid may be lifted together with the fill-pipe and other equipment projecting downwardly from the lid.  After the lid has been drilled and tapped, it is refitted to the tank and the tank then has to be subjected to a pressure test, in order to ensure that a perfect seal has been formed between the tank lid and the neck flange.  Once tested, the pipe-work and services are re-made to the tank lid, and then the tank has to be completely drained of water, before it can be placed back in service.  Moreover, the water will be contaminated and so has to be disposed of with considerable care.
	It will be appreciated that the above procedures take a most considerable time and may be performed only by skilled personnel; a tank typically is out of service for one to three days if the lid has to be removed, for any reason.  The effective cost to the garage proprietor is thus relatively high."
5.  The alternative process disclosed in the prior art is then described in this way:
"Though hole cutters including a threaded portion for tapping a cut hole are known (for example from JP-A-57184658), these have a pilot drill which leads the hole cutter.  Consequently, as soon as the pilot drill penetrates the workpiece (a pipe, in the case of JP-A-57184658), the hole-cutting operation is exposed to any vapour in the pipe.  This tool is thus quite unsuitable for use in a hazardous environment, such as the cutting of a threaded hole through the lid of a petrol tank."
6.  The specification then states:
"It is a principal aim of the present invention to provide both a method of an apparatus for forming a tapped hole through a metal plate which method and apparatus are particularly suitable for use on an underground petrol tank, and which allow the drilling and tapping of the hole through, for example, the tank lid without the need to remove the lid from the tank itself."
7.  There follows the consistory clauses, the first of which is stated to be a first aspect of the invention.  It is the method part of the invention.  In summary, the first aspect is provided by a method of forming a threaded hole through a tank lid without its removal by using a combined tap and rotary hole cutter, described as a "centre-less hole cutter", while an inert atmosphere is maintained on the side of a plate from which the cutting started.  The specification then turns at column 3 line 35 to "another aspect" of invention which is the tool.  In basic form it comprises a tapered tap, a centre-less rotary hole cutter, and means to rotate and feed the cutter and tap.  

8.  The design of a conventional cutter is then described as a prelude to an explanation of the advantage of using a centre-less hole cutter:
"A conventional design of a rotary hole cutter has a cylindrical wall formed with cutting teeth at its leading circular edge, the cylindrical wall being mounted on or integrally-formed with a circular end wall through which a drill co-axially extends, the cutting end of the drill being ahead of the teeth of the hole cutter.  In this way, the drill forms a pilot hole through the plate to be cut and then serves to centre the hole cutter itself.  However, penetration of the plate by the drill opens the tank even before the hole cutter has started to cut the plate.  By using a centre-less hole cutter (that is, a hole cutter not having a drill for forming a pilot hole), this early opening of the tank is obviated."
9.  The specification goes on:
"It is very difficult to prevent a conventional design of hole cutter but not provided with a pilot drill from wandering during the early stage of rotary cutting, unless rigid support can be provided for, and immediately adjacent, the hole cutter.  However, it has now been determined that by furnishing a resilient mounting arrangement for the hole cutter, as defined above, the tendency for the hole cutter to wander is greatly reduced and it is possible to cut a hole using the tool of this invention more or less exactly where required, even when the hole cutter is mounted on the leading end of a tapered tap, and with the nearest bearing giving radial location for the hole cutter being above the tap itself."
10.  The specification continues, with the aid of four figures to describe an apparatus suitable for use when carrying out the invention.  Figure 1 shows the rig; figure 2 the slide-head assembly and figure 3 shows a hole cutting and tapping tool supported by the rig of Figure 1.  As this appeal is concerned with the method claims, only Figure 3 is annexed to this judgment.  

11.  The hole cutter is shown generally as 50.  It has teeth, 51, and a magnet, 57, which attracts the part of the tank that is cut, thereby preventing it falling into the tank.  An inert gas such as CO2 is fed through a port, 66, into the chamber formed by the mounting plate, 52, and the ring, 65.  The cutter 50 is rotated by a drive shaft.  It contains a reamer section, 60, followed by tap sections, 61, 62 and 63, which are contained within the sleeve, 53.  

12.  Having described the method of use of the apparatus, the specification states:
"In the above way, a hole is cut through the tank lid 11, in the presence of an inert atmosphere which effectively removes the risk of an explosion.  The tank lid is opened only at the moment the hole cutter penetrates the lid, and the cut disk of the lid is held by the magnet 57, so preventing the disk (which may be at least warm) falling into the tank."

13.  Claims 1, 2, 4 and 5 are alleged to have been infringed and to be valid.  They are set out below together with claims 6 and 7 which were referred to by the parties in their submissions on infringement.
"1.  A method of forming a threaded hole through a plate (11) such as a tank lid, comprising advancing a rotary hole-cutter into the plate to form a circular hole therethrough, continuing to advance the hole-cutter beyond the plate and following the hole-cutter into the cut hole with a tapered tap (55) having a required thread form whilst rotating the tap to form a thread in the hole, characterised in that the circular hole is formed with  centre-less hole cutter (50, 51) and in that an inert atmosphere is maintained on the side of the plate (11) from which the cutting was commenced, in the region of the hole being cut through the plate both during the cutting and subsequent tapping thereof.

2.  A method according to Claim 1, in which the inert atmosphere is maintained by surrounding the hole-cutter (50, 51) and the tap (55) with a sleeve (23) which also bears on the plate, and supplying an inert gas to the interior of the sleeve (23).

...

4.  A method according to any of the preceding Claims, in which the inert atmosphere maintained in the region of the hole being cut is one of nitrogen or carbon-dioxide.

5.  A method according to any of the preceding Claims in which the plate (11) through which the tapped hole is to be formed is the lid of a subterranean petrol storage tank.

6.  A tool for cutting a threaded hole through a plate such as a tank lid and including a tapered tap (55) characterised in that the tool has a centre-less rotary hole-cutter (50, 51) and means (53, 54, 56) mounting the hole-cutter substantially co-axially on the leading end of the tap, which means transfers rotary drive from the tap (55) to the hole-cutter (50, 51) and permits the axis of the hole-cutter to move resiliently out of alignment with the axis of the tap.

7.  A tool as claimed in Claim 6, wherein said mounting means includes a resilient pad (56) disposed between the leading end face of the tap (55) and a rear face (52) of the hole-cutter (50)."				

Infringement
14.  At trial the respondents accepted that what was called method 1 infringed claim 1, if that claim was valid.  They contended that it was first used in July 1997 and was superseded in December 1997 by method 2.  That method was used until about the middle of February 1998 when method 3 was adopted.  The appellants do not allege that method 3 infringes as it uses a pilot drill which penetrates into the tank before the hole cutter has completed cutting.  It follows that the dispute on the infringement relates to method 2 and in particular whether a "centre-less hole cutter" was used.  

15.  In method 1, a cutter like that described in the patent was used.  The respondents gave evidence that it suffered from the defect that the cutter tended to wander to an unacceptable extent.  To avoid this, the defendants used a retractable probe or spindle within the cutting tool.  The judge described its action and use in this way:
"The defendants sought to overcome this problem by fitting in the middle of the cutter what may be described in a neutral way as a probe or pointed spindle, the function of which is to secure the lateral portion of the cutter and control the tendency to wander.  In this respect the probe or spindle performed the same function as a pilot drill.  In the example produced in court the probe or spindle, unlike a drill, had smooth sides, but its tip was shaped in the manner of a countersinking bit used for drilling a recess for a screw head.  This would undoubtedly pierce the surface of the part in which the hole was being cut, and by means of the purchase so obtained, would secure the location of the cutter until the stage at which the cutter would itself have penetrated deep enough to prevent wandering.  The probe or spindle was not, however, intended to pass through the part being cut in the way that a normal pilot drill would.  This was prevented by a means of retracting the probe or spindle before full penetration was effected.  In early versions of the tool using Method 2 this was done by allowing the probe or spindle to withdraw into the tool by pressure against a grub screw and spring.  In a later version a somewhat more elaborate withdrawal mechanism was used.  Nothing turns on the precise form of the two mechanisms.
	Except in respect of the probe or spindle Method 2 was substantially the same as Method 1.  Thus the tool was to operate within a shroud filled with inert gas.  According to the defendants it was used from about the middle of January 1998 until the middle of February 1998."   		

16.  The judge accepted the submission of the respondents that the cutter used in method 2, with its retractable spindle or probe, was not within the ambit of claim 1 as it was not a centre-less hole cutter as claimed.  He said:
"While the term "centre-less hole cutter" does not appear to be a term of art in general use, this fact presents no difficulty in discovering the meaning of the term.  In my view the patent specification provides, in this respect, its own technical dictionary.  I refer in particular to the sentence, which I have already quoted, which states
'By using a centre-less hole cutter (that is, a hole cutter not having a drill for forming a pilot hole), this early opening of the tank is obviated.' (emphasis added)
	In my view a hole is within the reference to a "pilot hole" even if it is a blind hole which does not pass right through the cover which is being cut.  The essential characteristics of a "drill for forming a pilot hole" are, to my mind, that it penetrates, either completely or partially, the object through which the hole is to be cut and that its purpose is to guide and locate the part of the tool which does the cutting.  
	I think that this view of the matter is supported by the next following paragraph of the specification.  This notes that
'It is very difficult to prevent a conventional design of hole cutter but not provided with a pilot drill from wandering during the early stage of rotary cutting, unless rigid support can be provided for, and immediately adjacent, the hole cutter.'
The remedy which is then suggested is not that of having a retractable pilot drill which does not fully penetrate the plate.  The assumption seems necessarily to be that there will be no pilot drill of any kind.  The method of preventing or reducing the tendency to wander which is propounded in the use of a resilient mounting arrangement for the hole-cutter, something quite different from drilling a blind hole or its equivalent.
	In my judgment the "centre-less hole cutter" referred to in Claim 1 is a rotary hole cutter which has as its centre nothing which is capable of making a hole or significant indentation in the plate which is to be cut.  The presence in the middle of the hole-cutter of a means of connecting it to the shaft which rotates the cutter or, as seen in some embodiments, a suspended magnet to catch the metallic disc which is removed by the cutter does not prevent the hole-cutting being "centre-less" for this purpose.  But I consider that the presence of a probe or pointed spindle which is intended to pierce the plate which is being cut, albeit not to pass right through it, does prevent the hole cutter being "centre-less".
17.  Mr Vanhegan, counsel for the appellants, criticised the approach to construction of the words "centre-less hole cutter" adopted by the judge and his conclusion.  He submitted that the judge had failed to adopt the approach to construction required by section 125 of the Patents Act 1977.  In my view that criticism may be justified in that the judge failed to refer to that section or the Protocol on Interpretation of Article 69 of the EPC or to any of the authorities which give guidance as to the correct approach to construction of claims since the passing of the 1977 Act.  

18.  For the first time infringement was defined in the 1977 Act.  Section 60 states that a person infringes a patent if he does an infringing act "in relation to the invention".  Section 125 of that Act provides that an invention shall be that specified in the claim "as interpreted by the description and drawings ... and the extent of the protection conferred by a patent ... shall be determined accordingly."  The extent of protection is not only important when considering whether an alleged infringement falls within the claim, but also when considering validity.  A patent will be invalid if the extent of protection includes within it the prior art or something which was obvious having regard to the prior art.  

19.  Section 125(3) requires the Protocol on Interpretation of Article 69 of the EPC to be applied.  It states:
"Article 69 should not be interpreted in the sense that the extent of the protection conferred by a European Patent is to be understood as that defined by the strict, literal meaning of the wording used in the claims, the description and drawings being employed only for the purpose of resolving an ambiguity found in the claims.  Neither should it be interpreted in the sense that the claims serve only as a guideline and that the actual protection conferred may extend to what, from a consideration of the description and drawings by a person skilled in the art, the patentee has contemplated.  On the contrary, it is to be interpreted as defining a position between these extremes which combines a fair protection for the patentee with a reasonable degree of certainty for third parties." 
The Protocol outlaws what can be termed strict literal and also liberal interpretation using the claims as a guideline.  The correct approach is to achieve a position between those extremes "which combines a fair protection for the patentee with a reasonable degree of certainty for third parties."  

20.  Strict literal interpretation using the drawings and specification gives to third parties the most certainty.  That has always been seen as being unfair to inventors and of course is outlawed by the Protocol.  However there must be a reasonable degree of certainty for third parties and therefore the language of the claim as interpreted in the light of the drawings and specification cannot be disregarded.  As pointed out by Hoffmann LJ in Société Technique de Pulversatur STEP v Emson Europe Ltd [1993] RPC 513 at 522 an integer of a claim cannot be just struck out because it does not make any difference to the inventive concept.  It may have been inserted by the patentee for some reason.  

21.  So far as the patentee is concerned it is important that the claim should be interpreted  in accordance with his intention.  A claim interpreted on the one hand too liberally can render the patent invalid and on the other too literally can allow third parties to avoid the monopoly.  

22.  The object of interpretation is to ascertain the intention of the author, in this case the patentee.  This involves examining the words of the claim through the eyes of a person to whom the specification is directed, in the context of the specification as a whole.  If the reader skilled in the art would have understood that the patentee intended that the claim should have a particular ambit, then to construe it as not confined to that ambit, by either strict or liberal construction, would be unfair to the patentee.  It is the patentee that chooses the words and to widen the ambit contrary to his intention could invalidate the patent and to restrict the ambit could allow use of the invention without payment.  

23.  As the task of the court is to ascertain objectively what meaning the words were intended to convey, the Improver questions, better called the Protocol questions, were proposed as an aid.  It is reasonable to infer, absent express words to the contrary, that the patentee intended to include within his monopoly what can be termed immaterial variants, in the sense that they were not material to the way the invention worked.  Also it is reasonable to infer that a patentee did not intend to include within the ambit of his monopoly a variant which had a material effect upon the way the invention worked, otherwise his claims could, to the detriment of the patentee, include variants which had little if anything to do with what he had invented.  However third parties have to be considered and therefore they should not be held to infringe if it was clear that such a variant was not intended to be within the ambit of the monopoly either because of the words chosen or because it would be seen to have materially affected the way the invention worked.  

24.  In Improver Corporation v Remington Consumer Products Limited [1990] FSR 181 Hoffmann J suggested at page 189 that the court when applying the Protocol should ask these questions:
"(1)  Does the variant have a material effect upon the way the invention works?  If yes, the variant is outside the claim.  If no-
(2)  Would this  (i.e. that the variant had no material effect) have been obvious at the date of the publication of the patent to a reader skilled in the art.  If no, the variant is outside the claim.  If yes -
(3)  Would the reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention.  If yes, the variant is outside the claim. 
	On the other hand, a negative answer to the last question would lead to the conclusion that the patentee was intending the word or phrase to have not a literal but a figurative meaning (the figure being a form of synecdoche or metonymy) denoting a class of things which included the variant and the literal meaning, the latter meaning, the latter being perhaps the most perfect, best-known or striking example of the class."
Hoffmann J went on to explain that the first two questions involved considerations of fact, but the last was a question of construction.  

25.  These questions do assist the court to construe a claim in accordance with the Protocol.  Question 1 envisages that the claim has an ambit wider than the literal meaning of the words so as to give fair protection for the patentee; but that is subject to the safeguards contained in it when considered with question 2.  Question 3 also provides a fair result for the patentee, namely avoidance of an unintended meaning.  It also requires attention to the purpose of the words thereby giving fair protection for third parties.  

26.  As Hoffmann J pointed out at page 191, the answer to the first question depends upon the level of generality at which one describes the way the invention works.  He said at page 192 "that the right approach is to describe the working of the invention at the level of generality with which it is described in the claim of the patent".  I agree.  

27.  The respondents supported the reasoning and conclusion reached by the judge.  They submitted that the patent contained a definition of the phrase "centre-less hole cutter" at column 3 line 54, namely a "hole cutter not having a drill for forming a pilot hole".  They submitted that the purpose of a pilot drill was to drill a hole to guide and locate and it mattered not whether the hole went through the part being drilled.  Thus a pilot drill need not penetrate, but may produced a blind hole.  Method 2 had a pilot drill which produced a blind hole and therefore did not come within the definition in the patent.  Further the variant, the probe, had a material effect upon the way the invention worked in that it prevented the cutter from wandering.  

28.  In my view the appellants are correct that the respondents' approach to construction does not accord with that required by the Protocol.  The patent has to be construed through the eyes of the skilled addressee.  He would be aware of the problem mentioned in the patent, when a further opening in a tank lid had to be made in an underground tank.  He would know that the standard procedure required removal of the tank lid as stated in the patent and that that was time consuming.  The patent refers to the prior art which uses a pilot drill which leads the cutter.  That is said to be unsatisfactory because "as soon as the pilot drill penetrates the work piece ... the hole cutting operation is exposed to any vapour ...".  The aim of the invention was to allow cutting with the tank lid in place.  That is done by the method of claim 1.  The passage starting at column 3 line 44 which contains the words relied on by the respondents as a definition have to be read as part of the whole paragraph.  The first sentence of that paragraph describes a conventional design of rotary hole cutter.  It had a drill co-axial to the cylindrical cutting teeth which preceded and penetrated the lid before the rotary cutting teeth had finished cutting.  The skilled addressee would realise that what was being described was conventional use which involved the lid being removed.  There follows a description of the basic idea of the invention, namely that penetration of the lid in advance of the rotary cutter should not happen.  In essence, use of a conventional cutter with its pilot drill which penetrated should be avoided.  As the patent states, "however, penetration of the plate by the drill opens the tank even before the cutter has started to cut the plate.  By using a centre-less hole cutter (that is a hole-cutter not having a drill for forming a pilot hole), this early opening of the tank is obviated."  At this stage of the description the patent is teaching that it is possible to cut openings without removal of the lid provided early opening of the tank is avoided.  To read the words "pilot hole" in that passage as including a blind hole, as advocated by the respondents and adopted by the judge, makes nonsense of the sentence.  A blind hole would not provide early opening.  Clearly the patentee did not have in mind a drill which did not penetrate into the tank.  He was concerned with the conventional cutters which had pilot drills which made a hole which did penetrate into the tank.  

29.  The patent goes on at column 3 line 57 to deal with wandering.  It points out that if you do away with the pilot drill (the skilled addressee would have in mind a drill which penetrated into the tank: see Evidence 2 page 33), it was difficult to prevent wandering unless rigid support was provided.  There follows the disclosure that the tendency to wander is reduced if a resilient mounting is used.  The skilled addressee would clearly understand that wandering could be avoided by rigid mounting and he would understand that the resilient mounting, claimed in claim 7, would help if rigid support was not provided.  The basis of the invention was the realisation that if you avoided penetration of the tank by removing the pilot drill from the conventional type of rotary cutter and surrounding the cutter with an inert gas, the lid could be cut without being removed.  

30.  The words "centre-less hole cutter", if read literally, mean a hole cutter without a centre.  Read in that way there is no infringement as the probe of the method 2 cutter is in the centre and has a centring action.  However method 2 takes the basic idea of the invention, namely cutting in situ using an inert surround without pre-penetration of the tank.  In effect method 2 provides an addition to the invention described in the patent.  

31.  Literal construction is outlawed by the Protocol.  It is necessary to give the claim an ambit which would provide fair protection for the patentee and reasonable certainty for third parties.  That is a difficult task but is, as I have stated, best achieved with the aid of the Improver questions.  
32.  (1)  Does the variant have any material effect upon the way the invention works?
That question requires consideration of a variant of the alleged invention.  In this case it is the probe used in method 2.  

33.  The respondents submitted that the probe did have a material effect on the way the invention worked in that it prevented wandering.  The appellants submitted that it did not as there was no penetration into the tank.  

34.  In my view the appellants are correct.  As pointed out by Hoffmann in Improver at page 191, the answer to the question depends upon the level of generality at which one describes the way the invention works.  Like him, I believe the generality should be at the level at which the invention is described in the claim.  

35.  Claim 1 is not concerned with wandering.  In general terms it sets out the basic invention, namely cutting in situ with an inert atmosphere.  It does not descend to any detail as to the construction of the tool other than it is a centre-less hole cutter with a tap.  The resilient pad which aids prevention of wandering is not mentioned until claim 7.  When so read, it is clear that the probe of method 2 will have no effect upon the invention.  There will not be any early opening of the tank during cutting.  Thus at the appropriate level of description method 2 works in the same way as the invention.  

36.  (2)  Would have it have been obvious to a man skilled in the art that the variant would work in the same way?
The respondents accept that if the answer to question 1 is no, then this question should be answered yes.  

37.  (3)  Would the skilled man in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention?
The respondents submitted that the skilled reader would understand that strict compliance was necessary as the centre-less hole cutter was an essential feature of the claim.  That submission does not provide the answer in this case.  Of course the centre-less hole cutter is an essential feature of the claim, but the issue is whether the words "centre-less hole cutter" should be construed so as to include the probe.  Thus the question requires consideration as to whether the skilled reader would understand that the patentee intended that a cutter with a retractable probe was to be excluded.  In my view he would not.  To the contrary, the skilled reader would interpret the claim as excluding anything which penetrated the tank lid before cutting had been completed.  The words "centre-less hole cutter" are not terms of art.  They have been used by the patentee to distinguish the conventional cutter described at column 3 line 44 and the prior art at column 2 line 18.  I therefore would answer this question, yes.  

38.  The answers to the Improver questions indicate that method 2 infringes, but they are only an aid to the decision which requires the claim to be interpreted to give fair protection and reasonable certainty.  The patent discloses as the basis of the invention a method of in situ hole cutting using an inert gas on the outside with a cutter and tap  with no pre-penetrating parts.  Fair protection would enable the patentee to monopolise just that, which of course includes method 2.  That also would give reasonable certainty.  A skilled reader would realise that method 2 used the inventive idea disclosed in the patent, albeit with an idea of how it could be done without using a rigid support or a resilient pad.  Thus he would realise that he was using the patentee's invention which he had sought to claim in words chosen to distinguish his cutter from what was conventionally used and the prior art mentioned in the patent.  

39.  I conclude that method 2 infringes claim 1 if it is valid.  That being so, it is admitted it infringes claims 2, 4 and 5.  

Validity
40.  The judge held that the patent was invalid as it was obvious having regard to common general knowledge and what was described as the Veeder Root use.  He rejected the attack based upon the Japanese patent No. 57-184658 of the Osaka Gas Company Ltd.  The appellants submitted that the judge was wrong to conclude that the patent was invalid as being obvious and the respondents supported the judge's conclusion and also raised again the Japanese patent.  

41.  A patent may be revoked under section 72 of the Patents Act 1977 if the invention is not a patentable invention.  A requirement of a patentable invention is that "it involves an inventive step" (see section 1).  Section 3 states that an invention shall be taken to involve an inventive step "if it is not obvious to a person skilled in the art, having to regard to any matter which forms a part of the state of the art by virtue only of section 2(2)".  Section 2(2) is in these terms:
"The state of the art in the case of an invention shall be taken to comprise all matter (whether a product, a process, information about either, or anything else) which has at any time before the priority date of that invention been made available to the public (whether in the United Kingdom or elsewhere) by written or oral description, by use or in any other way."	
The matters relied on as forming part of the state of the art have to be pleaded.  In this case the respondents relied inter alia upon the Veeder Root use and the Japanese patent together with what is called common general knowledge.  

42.  As I pointed out in Beloit Technologies Inc v Valmet Paper Machinery Inc [1977] RPC 489 at page 494:
"It has never been easy to differentiate between common general knowledge and that which is known by some.  It has become particularly difficult with the modern ability to circulate and retrieve information.  Employees of some companies, with the use of libraries and patent departments, will become aware of information soon after it is published in a whole variety of documents; whereas others, without such advantages, may never do so until that information is accepted generally and put into practice.  The notional skilled addressee is the ordinary man who may not have the advantages that some employees of large companies may have.  The information in a patent specification is addressed to such a man and must contain sufficient details for him to understand and apply the invention.  It will only lack an inventive step if it is obvious to such a man.  
	It follows that evidence that a fact is known or even well-known to a witness does not establish that that fact forms part of the common general knowledge.  Neither does it follow that it will form part of the common general knowledge if it is recorded in a document.  As stated by the Court of Appeal in General Tire & Rubber Co. v. Firestone Tyre & Rubber Co. Ltd [1972] RPC 457, at page 482, line 33:

"The two classes of documents which call for consideration in relation to common general knowledge in the instant case were individual patent specifications and 'widely read publications'.  

As to the former, it is not clear that individual patent specifications and their contents do not normally form part of the relevant common general knowledge, though there may be specifications which are so well known amongst those versed in the art and upon evidence of that state of affairs they form part of such knowledge, and also there may occasionally be particular industries (such as that of colour photography) in which the evidence may show that all specifications form part of the relevant knowledge.  

As regards scientific papers generally, it was said by Luxmoore J in British Acoustic Films (53 RPC 221 at 250):

"In my judgment it is not sufficient to prove common general knowledge that a particular disclosure is made in an article, or series of articles, in a scientific journal, no matter how wide the circulation of that journal may be, in the absence of any evidence that the disclosure is accepted generally by those who are engaged in the art to which the disclosure relates.  A piece of particular knowledge as disclosed in a scientific paper does not become common general knowledge merely because it is widely read, and still less because it is widely circulated.  Such a piece of knowledge only becomes general knowledge when it is generally known and accepted without question by the bulk of those who are engaged in the particular art; in other words, when it becomes part of their common stock of knowledge relating to the art."

And a little later, distinguishing between what has been written and what has been used, he said:

"It is certainly difficult to appreciate how the use of something which has in fact never been used in a particular art can ever be held to be common general knowledge in the art."

Those passages have often been quoted, and there has not been cited to us any case in which they have been criticised.  We accept them as correctly stating in general the law on this point, though reserving for further consideration whether the words 'accepted without question' may not be putting the position rather high: for the purposes of this case we are disposed, without wishing to put forward any full definition, to substitute the words 'generally regarded as a good basis for further action.'"
43.  The appellants submitted the judge had wrongly assumed that what was known formed part of the common general knowledge.  He had also failed to adopt the structured approach necessary to decide a case of obviousness and that had led him into the trap of hindsight reasoning or being wise after the event.  That is a difficulty that arises in patent cases.  As Lord Russell said in Non-Drip Measure Company Ltd v Strangers Ltd 60 RPC 135 at 142:
"Nothing is easier than to say, after the event, that the thing was obvious and involved no invention.  The words of Moulton LJ (British Westinghouse Co v Braulik) may well be called to mind in this connection - 'I confess' (he said) 'that I view with suspicion arguments to the effect that a new combination bringing with it new and important consequences in the shape of practical machines, is not an invention, because, when it has once been established, it is easy to show how it might be arrived at by starting from something known, and taking a series of apparently easy steps.  This is ex post facto analysis of invention is unfair to inventors and in my opinion is not countenanced by English patent law."
44.  To similar effect was the statement of Lord Diplock in Technograph Circuits Ltd v Mills & Rockley (Electronics) Ltd [1972] RPC 346 at page 362:
"The cross-examination of the respondents' expert followed with customary skill the familiar 'step by step' course.  I do not find it persuasive.  Once an invention has been made it is generally possible to postulate a combination of steps by which the inventor might have arrived at the invention that he claims in his specification if he started from something that was already known.  But it is only because the invention has been made and has proved successful that it is possible to postulate from what starting point and by what particular combination of steps the inventor could have arrived at his invention.  It may be that taken in isolation none of the steps which it is now possible to postulate, if taken in isolation, appears to call for any inventive ingenuity.  It is improbable that this reconstruction a posteriori represents the mental process by which the inventor in fact arrived at his invention, but, even if it were, inventive ingenuity lay in perceiving that the final result which it was the object of the inventor to achieve was attainable from the particular starting point and in his selection of the particular combination of steps which would lead to that result."		
45.  I believe the appellants are correct that the judge failed to distinguish between what was known and what formed part of the common general knowledge.  I suspect that this was because he failed to adopt the structured approach advocated by Oliver LJ in Windsurfing Inc v Tabur Marine (Great Britain) Ltd [1985] RPC 59 at page 73:
"There are, we think, four steps which require to be taken in answering the jury question.  The first is to identify the inventive concept embodied in the patent in suit.  Thereafter, the court has to assume the mantle of the normally skilled but unimaginative addressee in the art at the priority date and to impute to him what was, at that date, common general knowledge in the art in question.  The third step is to identify what, if any, differences exist between the matter cited as being "known or used" and the alleged invention.  Finally, the court has to ask itself whether, viewed without any knowledge of the alleged invention, those differences constitute steps which would have been obvious to the skilled man or whether they require any degree of invention."
46.  The judge concluded that the invention was obvious having regard to the common general knowledge which was possessed by the notional skilled man at the priority date.  However there was no evidence that a combined tap and cutter formed part of the common general knowledge of the person to whom the patent was directed.  The evidence, as the judge pointed out, was that such a combined tool had been described in the 1992 edition of a book as a "recent development", but was not described in the 1989 edition.  To that had to be added the evidence of Mr Gascoigne that his company had combined taps and cutters and at the date of the trial they sold about 50 a month.  He said that combined cutters and taps had been offered for sale in 1993, but he did not know whether they had been advertised.  That evidence establishes use, but does not establish, to the standard required in the extract from Beloit that I have cited above, that such a tool was part of the common general knowledge.  

47.  Use of inert gas was known, but there was no evidence of any use of such gas on the outside of a tank during drilling except by Veeder Root.  But it was not established that the Veeder Root use formed part of the common general knowledge.  No doubt it formed part of the state of the art, but that was all.  

48.  With that in mind, I must approach the issue of obviousness based upon common general knowledge using the structured approach set out in Windsurfing.  

49.  The inventive concept is a method of forming a threaded hole in a tank using a combined tap and hole cutter, an inert gas on the outside and a rotary cutter without pre-penetration by a pilot drill.  

50.  The skilled man would know of inert gas, rotary cutters and taps.  The method used in the past involved filling the tank with water, taking off the lid and then cutting the hole using a cutter with a penetrating pilot drill, tapping and then replacing the lid.  

51.  The differences between the method of claim 1 and those which formed the common general knowledge are that the hole is cut without the lid being removed, inert gas is applied to the outside, a combined tap and cutter is used and the cutter does not have a penetrating pilot drill.  

52.  Obviousness is a jury-type question and therefore this Court should be slow to differ from the decision of the judge unless he erred in principle.  In this case I believe he did in that he failed to differentiate between what was known and what was common general knowledge.  

53.  The change from what was used before was not established to be obvious.  Professor Childs, the expert called by the respondents to give evidence, was not the notional skilled person.  He was a skilled engineer, not the notional unimaginative man who lacked the ability to invent.  As to the evidence of Dr Michels, that upon his construction of the claim, he did not believe that the invention was obvious.  His cross-examination adds nothing as it adopted the approach criticised by Lord Diplock in the passage I have quoted from Technograph.  

54.  In my view the judge fell into the trap of hindsight reasoning.  The change from what had gone before could have been suggested some years before 1993.  All the elements to arrive at the invention were available.  If it had been an obvious idea, why had it not been suggested before 1993, particularly as its advantages are evident once the answer is known?  In my view the words of Lord Russell are apposite to the present case.  

55.  The attack based upon Veeder Root has more substance.  Veeder Root are a large supplier of tanks and associated equipment such as gauges.  They had need to fit gauges to tanks which had been installed.  Over a period of about a year or so they developed in the late 1980's a process in which a hole could be drilled in the top of the tank without the tank lid being removed.  This was done using a rig supporting a drill positioned over the tank.  The next step was to place a shroud onto the tank to which was attached a carbon dioxide supply.  Thereafter a conventional twist drill was lowered into the shroud which was flooded with CO2.  The drill contacted the lid and drilled through it.  The drill was then withdrawn and a tap was substituted to produce the thread.  

56.  The differences between the Veeder Root process and the invention are the use of a combined tap and cutter and the use of a centre-less hole cutter.  

57.  For my part I did not find persuasive the submission of the appellants that it was inventive to combine the tap and the cutter.  I accept that ordinarily a combined tap and cutter would not be desirable as the evidence established that the drill would wear out quicker than the tap.  However to screw them together, rather than using them one after the other, appears to me to be an obvious alternative.  That conclusion is supported by the evidence of Mr Cox of Veeder Root that they had used such an arrangement in the past and that combined cutters and taps had been made.  

58.  The respondents case that it was obvious to move from the Veeder Root drill to a centre-less hole cutter has the attraction of simplicity.  They submitted that the Veeder Root system was designed to drill a small hole to accommodate a gauge.  If you wanted to drill a hole for a pipe, it was obvious to move to a rotary cutter and there could be nothing inventive in taking a standard rotary cutter, which did not have a pilot drill, and use it in just the same way as Veeder Root had used their conventional twist drill.

59.  As I have said that submission has the attraction of simplicity which at times during the case I found attractive.  The invention appears obvious once the destination is known; but in the end I have concluded that it had not been established that it would have been obvious to the skilled person in 1993.  At that date the skilled person would have had in his mind the standard process which required the lid to be removed which was then drilled with a rotary cutter having a penetrating pilot drill.  Having seen the Veeder Root process, the skilled person would appreciate that an inert gas on the outside was an advantage, but I am not convinced it would have been obvious to him to move away from the type of cutter that had been used in the past for producing large holes in underground tanks nor that in situ cutting of large holes was possible.  Certainly Veeder Root never thought of it despite their knowledge and position in the market.  I accept that Veeder Root's business required the drilling of small holes for their gauges, but they were well aware that their customers had a need for larger holes to be made in tanks in the ground.  Mr Cox of Veeder Root, when he became aware of the patented process, considered that it was "neat".  Since it has been commercialised, Veeder Root have referred their customers to Bortec Limited.  They have also sought to purchase the patent rights.  Dr Michels was of the view that it was not obvious to move from Veeder Root to the commercial and safe procedure claimed in the patent.  Mr Pick who was in 1993 the senior licensing officer of the Licensing Authority for Greater London regarded the patented procedure as "a considerable step forward".  He had been aware of a process for drilling small holes in tanks, no doubt the Veeder Root process.  

60.  Japanese patent No.57-184658 was applied for on 10th November 1976.  It relates to an invention for a "pipeline drill".  The specification states that the invention is concerned with the oil supply technology in pipeline drills and for drilling holes and hole threading in pipelines which transport gas, water and the like.  It points out that during drilling a lubricating oil supply is required to keep the drill cool and to avoid resistance.  The prior art devices are said not to deal with the swarf generated with the result that it mingles with the oil damaging the drill blade and precluding accurate tapping.  The claim of the invention is that it provides a pipeline drill which automatically supplies oil to the cutting area and thereby reduces the swarf.  

61.  As pointed out by the judge the two figures may show a rotary hole cutter, but the Japanese, as translated, does not so state.  It indicates an oil reservoir above a drill bit consisting of a main drill bit and a pilot drill bit.  It seems that the pilot drill bit will penetrate the pipe before the main drill bit has completed its task.  The whole arrangement was held in place on the pipeline by chain around the pipe.  

62.  The judge held, in the light of the description as translated, that the Japanese patent did not disclose use of a centre-less hole cutter nor a tapping tool joined with a drill.  He also held that the Japanese patent would not assist the skilled man to arrive at the combination of claim 1 in view of the emphasis placed on the lubricant.  

63.  Mr Micklethwait, who appeared on behalf of the respondent, submitted that the Japanese patent disclosed a rotary cutter of the type claimed in the patent in suit.  He went on to refer to the judgment of Laddie J in Brugger v Medic-Aid Ltd [1996] RPC 635 which drew attention to the policy behind the law on obviousness.  A trader should not be prevented by a patent monopoly from doing something which was obvious even though that might not be thought commercially worthwhile.  He submitted that claim 1 lacked invention over the disclosure in the Japanese patent specification.  

64.  I agree with the judge that the Japanese patent specification does not disclose a centre-less hole cutter, nor does it disclose use of an inert gas.  In my view he was also right to reject the respondents' attack based upon this Japanese patent.  The skilled person would realise that the Japanese patent was concerned with the provision and use of lubricant during drilling into pipes.  To arrive at the invention it would be necessary to reject the basic teaching of the Japanese patent and use the oil reservoir for the inert gas.  I can see no reason why the skilled person should do so unless he had the invention of the appellants in mind. 

65.  For the reasons that I have given I have concluded that the attack upon the patent has not been established.  

Conclusion
66.  I would allow the appeal as I have concluded that method 2 infringes the patent and that the patent is valid.  

SEDLEY LJ:
67.  I agree with Aldous and Mance LJJ that the appeal on the validity of the claims succeeds.  

68.  On the question of infringement I agree with the judgment of Mance LJ.  While I defer entirely to the exposition of the law given by Aldous LJ, the critical question is in the end one of first impression: is the appellants' device a centreless hole-cutter?  In my judgment it is not.  It has a central drill as its locating device.  The fact that the drill does not penetrate the tank or other object does not, it seems to me, makes it any the less a centring device.  

69.  Like Mance LJ, and for the reasons more fully spelt out by him, I would therefore dismiss the appeal on infringement of method 2.  

MANCE LJ:
70.  I have had the benefit of reading in draft the judgment delivered by Aldous LJ.  In it he sets out the relevant facts and legal principles in a way which I gratefully adopt.  It is with some diffidence that, in this field, I find myself in disagreement with him to a limited, but critical extent.

71.  I agree with Aldous LJ that the appellants succeed in their appeal with respect to the validity of the patent.  The appellants’ patent taught that there was advantage in a centre-less annular cutter, whereby the first penetration of the tank would be by the annular cutter, with a shield of inert gas around it.  On account of that perceived advantage, it forewent the use of a conventional rotary hole cutter.  The appellants submit that the relevant inventive step involved in claim 1 consisted in (a) the introduction of a combined cutter/tap, (b) the centre-less character of the annular cutter, so that the cutter formed the first hole, (c) the maintenance of an inert atmosphere on the side of the plate from which cutting took place and/or (d) the combination of these matters, in each case in the context of the formation and sealing of a new opening in the lid of a tank containing potentially inflammable gases.

72.  The judge held that these integers were (whether taken individually or in combination) matters of common general knowledge, or obvious to the notional skilled man on the basis of common general knowledge, and that the patent did not therefore involve any novelty.  Alternatively, he held that, insofar as they were not, they involved an obvious development of other prior art in the form of the Veeder Root patent.  Aldous LJ points out that the judge did not clearly adopt the structured approach advocated by Oliver LJ in Windsurfing Inc. v. Tabur Marine (Great Britain) Ltd [1985] RPC 59, 73 or refer to the discussion of the concept of common general knowledge in authority such as Benoit Technologies Inc. v. Valmet Paper Machinery Inc. [1977] RPC 489, 494.

73.  I would not however myself interfere with the judge’s conclusion that the use of a combined annular cutter and tap was in 1993 part of common general knowledge or obvious in contexts other than the present.  The evidence given by Mr Gascoigne seems to me, as it seemed to the judge, to have been persuasive on that point.  But the use of a combined cutter and tap without any centring mechanism in the present context of creating and sealing a new opening in the lids of tanks containing potentially inflammable gases is a different matter.  No one had, so far as appears, used or thought of such an approach in this context previously.  Nor was it, I think, obvious to a skilled man, even taking into account the prior state of the art in the form of the Veeder Root system.  That system involved a penetrating drill operating within a shroud holding inert gas, and was developed and confined in relation to small holes.  The conventional design of a rotary hole cutter, as described in the patent itself, also involved use a pilot drill penetrating the tank.  The function of the pilot drill in such a cutter is not to penetrate the tank - that is no more than its ancillary effect - but to centre the cutter and prevent it wandering or shattering.  The problem of wandering is mentioned in the patent.  The respondents experienced the problem of shattering with their method 1.  The inventive step involved in claim 1 was the recognition that, despite the potential problem of (in particular) wandering, there could be advantage in use of a centre-less annular cutter.  It was not common general knowledge, nor obvious in the light of common general knowledge, that a centre-less cutter and tap could be used with advantage in such a context.  In that respect, claim 1 did in my judgment involve patentable novelty.

74.  The critical question is whether claim 1 was infringed by the respondents’ method 2.  Aldous LJ sets out the passages in which the judge described this method and concluded that claim 1 was not infringed.  Method 2 involves a combined annular cutter and tap in the centre of which was a smooth-sided probe or spindle, with a tip shaped like a countersinking bit used for drilling a recess for a screw head.  This tip drills a “blind” hole, so serving to prevent wandering or shattering of the cutter, but is prevented from penetrating the tank plate by a device causing it to retract while the annular cutter proceeds.  It serves the function of a drill in a conventional rotary hole cutter, that is to prevent the cutter wandering or shattering, but does so without fully penetrating the relevant tank or plate.

75.  The relevant principles of interpretation are found in the Protocol on Interpretation of Article 69 applicable under s.125(3) of the Patents Act 1977, and authorities, particularly Improver Corp. v. Remington Consumer Products Ltd. [1990] FSR 181, offering guidance on their application.  The Protocol reflects an approach which was already part of English law as it had been expounded by Lord Diplock in Catnic v. Hill & Smith [1982] RPC 183, 242:
“My Lords, a patent specification is a unilateral statement by the patentee, in words of his own choosing, addressed to those likely to have a practical interest in the subject matter of his invention (i.e. “skilled in the art”), by which he informs them what he claims to be the essential features of the new product or process for which the letters patent grant him a monopoly.  It is those novel features only that he claims to be essential that constitute the so-called “pith and marrow” of the claim.  A patent specification should be given a purposive construction rather than a purely literal one derived from applying to it the kind of meticulous verbal analysis in which lawyers are too often tempted by their training to indulge.  The question in each case is whether persons with practical knowledge and experience of the kind of work in which the invention was intended to be used, would understand that strict compliance with a particular descriptive word or phrase appearing in a claim was intended by the patentee to be an essential requirement of the invention so that any variant would fall outside the monopoly claimed, even though it could have no material effect upon the way the invention worked.”
76.  Lord Diplock continued with the passage which is the foundation for the Improver questions:
“The question, of course, does not arise where the variant would in fact have a material effect upon the way in which the invention worked.  Nor does it arise unless at the date of the publication of the specification it would be obvious to the informed reader that this [i.e. that the variant could have no material effect upon the way the invention works] was so.  Where it is not obvious, in the light of then-existing knowledge, the reader is entitled to assume that the patentee thought at the time of the specification that he had good reason for limiting his monopoly so strictly and had intended to do so, even though subsequent work by him or others in the field of the intervention might show the limitation to have been unnecessary.  It is to be answered in the negative only when it would be apparent to any reader skilled in the art that a particular descriptive word or phrase used in a claim cannot have been intended by a patentee, who was also skilled in the art, to exclude minor variants which, to the knowledge of both him and the readers to whom the patent was addressed, could have no material effect upon the way in which the invention worked.”

77.  These passages in Lord Diplock’s speech in Catnic underline the fact that, in this context as elsewhere in the law, the issue of construction is ultimately a unitary one.  The various matters arising under the second quoted paragraph, which were reformulated by Hoffmann J. in Improver as the three Improver questions, aim simply to assist in arrival at the proper purposive and contextual interpretation.  They assist, in particular, to decide “whether a feature embodied in an alleged infringement which fell outside the primary, literal or acontextual meaning of a descriptive word or phrase in the claim (“a variant”) was nevertheless within its language as properly interpreted” (Improver, per Hoffmann J. at p.189).  “In the end, therefore,” as Hoffmann J went on to say:
“The question is always whether the infringement is covered by the language of the claim.  This, I think, is what Lord Diplock meant in Catnic when he said that there was no dichotomy between “textual infringement” and infringement of the “pith and marrow” of the patent and why respectfully think that Fox LJ put the question with great precision in Anchor Building Products Ltd. v. Redland Roof Tiles Ltd. (23rd November 1988, unrep’d) when he said the question was whether the absence of a feature mentioned in the claim was “an immaterial variant which a person skilled in the trade would have regarded as being within the ambit of the language” (My emphasis).  It is worth noting that Lord Diplock’s first two questions, although they cannot sensibly be answered without reference to the patent, do not primarily involve questions of construction: whether the patent would make a material difference to the way the invention worked and whether this would have been obvious to the skilled reader are questions of fact.  The answers are used to provide the factual background against which the specification must be construed.  It is the third question which raises the question of construction and Lord Diplock’s formulation makes it clear that on this question the answers to the first two questions are not conclusive.  Even a purposive construction of the language of the patent may lead to the conclusion that although the variant made no material difference and this would have been obvious at the time, the patentee for some reason was confining his claim to the primary meaning and excluding the variant.  If this were not the case, there would be no point in asking the third question at all.”
78.  Every claim must be interpreted in the context in which it appears.  Although the scope of the monopoly claimed is to be found in the relevant claim, the language of the claim must, as the Protocol indicates, be interpreted in the light of the description and drawings.

79.  A stated characteristic of claim 1 is that it involves formation of a circular hole with a centre-less hole cutter.  In that connection, reference is made to the numbers 50 and 51 appearing on figure 3, which shows a hole cutting and tapping tool.  The numbers 50 and 51 show the annular teeth and a magnet hanging in the ring which they form.  The general description of the patent says in relation to the figures:
“By way of example only, the various aspects of this invention will be described in further detail referring to the accompanying drawings ….” 
80.  Thus far, the “centre-less” aspect of claim 1 suggests an annular cutter, with no cutting or guiding device in its centre.  When one reverts to the description for fuller background, it amplifies the reason for this aspect in columns 3 and 4.  First, it mentions that a conventional rotary hole cutter would have a central drill the cutting head of which would be “ahead of the teeth of the hole cutter”.  Next it acknowledges that
“In this way, the drill forms a pilot hole through the plate to be cut and then serves to centre the hole cutter itself.”
81.  It proceeds to identify the perceived concomitant disadvantage, namely that the drill’s penetration opens the plate before the hole cutter has even started to cut the plate.  Then, it states the essence of the inventive step involved in the appellants’ device:
“By using a centre-less hole cutter (that is, a hole cutter not having a drill for forming a pilot hole), this early opening of the tank is obviated.”
82.  Immediately thereafter, the description recognises the concomitant problem, and proposes a solution:
"It is very difficult to prevent a conventional design of hole cutter but not provided with a pilot drill from wandering during the early stage of rotary cutting, unless rigid support can be provided for, and immediately adjacent to, the hole cutter.  However, it has now been determined that by furnishing a resilient mounting arrangement for the hole cutter, as defined above, the tendency for the hole cutter to wander is greatly reduced and it is possible to cut a hole using the tool of this invention more or less exactly where required, even when the hole cutter is mounted on the leading end of a tapered tap, and with the nearest bearing giving radial location for the hole cutter being above the tap itself.”
The description goes on to explain that the “invention further provides a rig” which includes “supporting means to support the tool”.

83.  Reading the claim against this background, it is to my mind clear that, when conceiving and describing their invention, the appellant patentees did not contemplate the introduction of any central device, serving to centre the hole cutter.  Either the idea of a centring device which did not pierce the integrity of the tank did not occur to them or, if it did, they put it aside for reasons which must have seemed good at the time.  As a result, their description of their invention proceeds on the basis that the perceived advantage of first penetration by the annular cutter would necessarily involve the disadvantage of lack of central stabilisation by any pilot drill.  They had in mind simply and solely a tool involving an annular cutter without any form of central device which would either penetrate or centre the cutter.  

84.  The inventiveness, such as it was, of the appellants’ claim 1 lay, as I have concluded, in the recognition that first penetration of a tank could be achieved by using an annular cutter, but by abandoning the conventional aspect of such a cutter consisting of a centring pilot drill.  That inventive step was fortified by the development of the feature of a resilient mount for the cutter (the subject of claims 6 onwards) in order to assist to overcome the concomitant problem of wandering to which it led.

85.  The respondents carried matters a stage further when they conceived the idea of using a central pilot drill or device which, by making a blind hole, would serve both to avoid full penetration and to centre the annular cutter.  Whether or not this itself involved any further inventive step, in my judgment, the patent, construed as a whole, demonstrates that it was not a step which the appellants themselves conceived, or at least contemplated as available or workable, or which was covered by the language which they chose to use.  Whether, now that this possibility has been drawn to their attention as a workable intermediate solution, they would like to have covered it, is a quite different matter.  Whether it would have been obvious as such to a hypothetical skilled person is also a different question.  The judge has not found, and there is no evidence to suggest, that a skilled person would, on reading the appellants’ patent, have realised that both the advantage of first penetration by the annular cutter and the disadvantage of lack of central guidance might be overcome simultaneously in the way that the respondents developed.  But, even if he had found this, the appellants’ patent must be interpreted purposively according to its intended scope.  If the appellants had seen this possibility, and intended to cover it, as a worthwhile development, I have no doubt that they would have expressed themselves differently and made that intention clear.

86.  The appellants rely upon the definition in the description of the patent:
“a centre-less hole cutter (that is, a hole cutter not having a drill for forming a pilot hole) [by use whereof] this early opening of the tank is obviated.”

87.  Reading the patent as a whole, what the appellants were there making clear was, firstly, that their rotary hole cutter operated without any central guiding or piloting device and, secondly, that it thereby obviated any early opening of the tank.  It is, as I have said, clear that the possibility that the second feature (obviating early opening) could have been achieved without adopting the first feature (a centre-less hole cutter) – by use of a partially penetrating, but guiding pilot drill – either did not occur to them at all or did not occur to them as a worthwhile development.  They therefore rejected the whole idea of any centrally located centring device.  It is in this sense that I, like the judge, would interpret their reference in claim 1 to a “centre-less” hole cutter.  All this is apparent in the description where the appellants went on, immediately after introducing and explaining that phrase, first to identify the concomitant disadvantage of wandering; and then to introduce the further inventive solution of “furnishing a resilient mounting arrangement for the hole cutter, as defined above” in order to address that problem.  If a “hole cutter, as defined above” included a hole cutter with a semi-penetrating and retractable centring drill, that problem would simply not arise and this solution would not be necessary at all.  It is only by looking at claim 1 in isolation that the appellants are now able to suggest that, despite the use of the word “centre-less”, claim 1 embraces the use of a semi-penetrating and retractable centring drill making a blind hole.  As a matter of construction, the background to the claim - to be found in the description and drawings - confirms that the appellants did not in claim 1 have in mind or cover a tool including such a device.  It would run contrary to the train of their inventiveness and thought-process if claim 1 were treated as preserving the possibility of a centring device consisting of a partially penetrating and guiding device.

88.  I turn to the three Improver questions, bearing always in mind that they are no more than aids to assist to arrive at the proper purposive construction.  The first question is whether the variant has a material effect upon the way in which the invention works.  If it has, the natural assumption is that the variant was not embraced within the patented invention.  Viewing claim 1 at the level of generality at which the patentee chose to describe his invention (cf Improver, 192, per Hoffmann J), the invention which it claimed involved the use of a centre-less hole cutter to achieve the first opening of the tank.  As I have said, a “centre-less” hole cutter is one which offers both advantage and potential disadvantage.  I see some scope for arguing that both should be taken into account in judging whether the variant has a material effect on “the way the invention works”.  But I am inclined to accept that what here matters is the intended advantage (namely, that the first opening was made by the annular cutter) rather than any concomitant disadvantage (namely, that the annular cutter might be prone to wander or shatter).  The disadvantage represented, if anything, a way in which the invention might fail to work, rather than the way in which (it was hoped) it would work.  Claim 1 either assumes that there is no real problem about ensuring the centring of the cutter and preventing wandering or shattering.  Or it simply leaves the problem to be addressed in later claims.  On this basis, it seems to me that the introduction of a pilot drill making a blind hole, to ensure centring and to avoid wandering or shattering may, for the purposes of claim 1, be regarded as a variant which is immaterial to the way in which claim 1 views the invention as working.  It addresses a potential problem, inherent in the way in which claim 1 works, but which claim 1 does not seek to address or resolve.  The answer to the first Improver question is on this basis in the negative and in the appellants’ favour.

89.  If so, it must follow that so too is the answer to the second Improver question.  That is whether it would have been obvious to a man skilled in the art that the variant would work in the same way.  A skilled man would appreciate that the way in which claim 1 worked was by ensuring that the first opening of a hole was by the annular cutter, and that this was equally so in the case of the variant.

90.  The third question is: Would the reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention? The reference to the reader skilled in the art cannot constitute an invitation to re-write or interpret the patent according to the language or scope that the patentee could or would reasonably have had in mind, had it only foreseen, or seen as workable, the variant now developed.  The hypothetical skilled person is not assumed to be skilled in patent law; he would not regard himself as free to disregard any apparent limitation in the patent, simply because a claim in wider generic terms might (at least later and with hindsight) be suggested.  The way in which the patent was here actually formulated, and the scope which it was actually given, may have derived from considerations internal to the appellants’ thinking which, however well- or ill-founded they may have been, were perceived by the appellant patentees as important.  Here, such considerations are apparent.  For whatever reasons, the appellants did not realise or consider that there was any or any workable solution, involving the use of a centrally positioned centralising drill or device, which would resolve the problem of penetration into the tank while at the same time avoiding the problem of wandering (and shattering).  The appellants’ inventiveness involved, but was limited to, the recognition that first penetration could usefully be achieved by the annular cutter.  They considered, and expressed themselves on the basis, that this must necessarily at the expense of lack of any centrally positioned centralising drill or device.  The language and scope of the whole of their patent reflects and recognises this limitation in their invention.  In these circumstances, a reader skilled in the art would have understood from the language of the claim that the patentees intended that strict compliance with the primary meaning of the phrase “centre-less” hole cutter was an essential requirement of the invention, because that was how the appellants at the time (whether or not with hindsight mistakenly) saw and expressed it.

91.  For the reasons that I have given, whether the issue of interpretation is viewed as a unitary exercise in identifying the proper purposive construction, or whether it is approached through the gateway of the three Improver questions which the judge did not mention, I consider that claims 1 to 5 in this patent did not embrace method 2 developed by the respondents.  Accordingly, while I agree with Aldous LJ that the appeal succeeds on the issue of the validity of those claims, I consider that it fails on the issue whether respondents’ method 2 infringed claims 1 to 5.

Order:  Appeal allowed in part.  Leave to appeal to the House of Lords refused.  No order for costs in the appeal.  The claimant to have 20% of their costs in the court below.
(Minute of Order provided by counsel.)

(Order does not form part of the approved judgment.)