Can complying with European practice render a UK patent invalid?
Those of you familiar with European patent practice will be intimately acquainted with the joy that is “two-part form”. This is where features known from prior art cited in a search or examination report are placed in a preamble to a claim, with novel features being placed after words such as “characterised by…”. While not compulsory, it is normally requested during prosecution. An amendment to place a claim in “two-part form” is usually accompanied by an amendment adding references to the prior art to an introductory portion of the patent specification. Case law from the European Patent Office deems that these amendments do not add subject matter.
As these amendments are so common, it is easy to assume that they are also valid under UK patent law. However, this may not be the case.
The Manual of Patent Practice (MPP – Section 76.14) states that:
There may be no objection to an amendment introducing information regarding prior art, provided it does not alter the construction of the claims of the patent in suit (Cartonneries de Thulin SA v CTP White Knight Ltd  RPC 6).
Note the language of “no objection” rather than a statement that this is allowable. The MPP goes on to state:
In Palmaz’s European Patents (UK) ( RPC 47, upheld on appeal  RPC 631) Pumfrey J stated that the practice, allowed by Advanced Semiconductor Products OJEPO 8/94 &  EPOR 97 (G 01/93) of adding an acknowledgement of prior art to the body of the specification and limiting the claim by reference to the prior art so acknowledged was too generally used in proceedings before the EPO to be challenged, but noted that caution must be exercised where the patentee himself described the prior art in terms which he proposes to use in the limitation of his claim.
In the High Court decision in Cartonneries De Thulin SA v CTP White Knight Ltd, Mr Justice Neuberger (as he then was), said that:
94. I ought perhaps add this. I would be reluctant to hold that the addition of a reference to the prior art in a patent constituted impermissible added matter. However, I accept that it could well be that, if the Court concluded that the way in which this subsequently added prior art was described in the relevant patent resulted in a different construction of a particular claim in the patent from that which the Court would otherwise have adopted, then it could well be that it constitutes added matter.
In the subsequent appeal, the Lord Justices found that an amendment to the claim based on a prior art citation added subject matter and ordered the patent to be revoked.
In Palmaz’s European Patents (UK), the late Mr Justice Pumfrey (as he then was) found that an amendment to limit a claim by reference to cited prior art would add subject matter by introducing an interpretation of the claims that was not derivable from the application as filed.
Where does this leave us?
Basically, for prosecution of UK applications the guidance is: do not amend the specification or claims to reference prior art cited later in prosecution. In particular: do not make changes to the claims that are only derivable from material in the the cited art.
When amending a European patent application that is destined for the UK, the guidance is: be careful. Make sure that the placing of the claim in two-part form can be unambiguously derived from the application as filed and keep discussion of the prior art to a minimum.
I think in most cases it would be relatively easy to argue that adding a prior art reference or placing in two-part form changes the interpretation of the claims. Whether this added subject matter would be decided on the facts but the matter is likely arguable, being open to a subjective reading of the specification. This offers an interesting strategy for UK litigation of granted EP(UK) patents that have been amended to two-part form according to EP practice; it may be worth adding a short added subject matter objection to any case for invalidity. Even if their hands are tied by common European practice, it would seem that the UK courts are receptive to revoking patents on this basis.