In the seminal UK case on claim construction, Kirin Amgen v Hoechst Marion Roussel, Lord Hoffmann, who gave the leading speech, commented that because Article 69 EPC focuses the scope of protection on the language of the claims, there was no doctrine of equivalents in Europe. Accordingly, unlike in the US where there is a doctrine of equivalents, there is no need to balance this with the further doctrine of ‘file wrapper estoppel’. He also went a little further, commenting that reference to the prosecution history generally for the purposes of construing patent claims in Europe was something which was not generally desirable. He said: “The courts of the United Kingdom, the Netherlands and Germany certainly discourage, if they do not actually prohibit, use of the patent office file in aid of construction. There are good reasons: the meaning of the patent should not change according to whether or not the person skilled in the art has access to the file and in any case life itself is too short for the limited assistance which it can provide.

Rohn and Hass v Collag

In a previous case (Rohm and Haas v Collag) the Court of Appeal had found guidance on reference to the prosecution history to be useful (given by the Dutch Supreme Court in Ciba-Giegy v Ote Optics). That guidance essentially said that the file history should only be referred to as a last resort where the claims remained open to interpretation after consideration of their meaning in the light of the description and drawings.

Accordingly, until very recently, the view in the UK had been that reference to the file history on the question of claim construction should only be permissible in very limited circumstances, and certainly not as a means to provide some form of estoppel similar to that in the US.

Activis v Lilly

However, in Activis v Lilly, Mr Justice Arnold recently referred to the file wrapper as part of his assessment of the meaning of the claims in issue. While he acknowledged that courts should be cautious in so doing, and he expressly recognized that there is no doctrine of file wrapper estoppel in the UK, the judge said: “Consideration of the prosecution file may assist in ensuring that patentees do not abuse the system by accepting narrow claims during prosecution and then arguing for a broad construction of those claims for the purpose of infringement.

In this case, during prosecution the patentee narrowed the claims of the application to overcome both clarity/sufficiency and added matter objections. In order to overcome these objections, the patentee ultimately restricted the claim to a preferred embodiment using a particular compound. The patent was duly granted. It was noted by Mr Justice Arnold that the examiner’s objections were neither challenged nor appealed, and that the patentee admitted that making the amendments “was a deliberate and conscious act”.

The judge ultimately construed the claims as being limited to the particular compound specified in the claims, as this provides the patentee “with fair protection and does not expose [the patentee] to the risk of the patent being invalid on the grounds of added matter and/or sufficiency. Construing the claim [any broader] would not provide a reasonable degree of certainty for third parties.

In reaching this conclusion, the judge applied several considerations as to why the claim should be so limited. One of these was the prosecution history, including the conduct of the patentee in seeking limiting amendments during prosecution, including why they were sought.

Conclusions from Activis v Lilly

While he acknowledged that there is no doctrine of file wrapper estoppel in the UK and that courts should be cautious before relying on the file wrapper for construction generally, Mr Justice Arnold does seem to have placed significant weight on both the file wrapper generally and, in particular, the conduct of the patentee, in construing the claims of the patent in issue.

File wrapper estoppel in the UK

This case is likely to go to appeal and it is difficult to predict the extent to which this aspect, of what is a long and detailed decision, will be affected by the Court of Appeal. Until such time as we know the answer to that question, it is difficult to predict whether this represents a shift in attitude of the UK courts on the use of the prosecution history in claim construction, and in particular how statements made in prosecution may be used to the detriment of the patentee.

It is certainly worth reminding ourselves that one should consider carefully both amendments and statements made during the prosecution since they may, whether expressly or implicitly, be used in the UK and elsewhere to restrict the ability of patentees to argue for a broad claim construction in subsequent litigation.