As you know, the US has a doctrine of equivalents. In order to balance this, a doctrine of "file wrapper estoppel" exists. This doctrine of prosecution history ("file wrapper") estoppel does not exist in the UK. However, it has always been possible to submit the file wrapper in UK court proceedings as an aid to construction of the claims. On the whole, though, UK courts have been reluctant to refer to the file wrapper.

However, in a recent wide ranging case in the pharma field, Actavis UK Ltd (and Others) v Eli Lilly & Company, [2014] EWHC 1511 (Pat), Justice Arnold did refer to the file wrapper to help interpret the claims. Specifically, although acknowledging that courts should be cautious before relying upon the file wrapper, Justice Arnold stated that "consideration of the prosecution file may assist in ensuring the 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 applicant (who became the patentee) narrowed the claims of the EP application to overcome a clarity/sufficiency objection and later an added matter objection. The Examiner stated that the claims of the application were so broad that they were not supported by the description (clarity) and that such breadth meant that the disclosure was insufficient (sufficiency). There were additional novelty and inventive step objections.

In order to overcome these objections, the applicant ultimately restricted the claim to a preferred embodiment using a particular compound. The case then went to grant. It was noted by Justice Arnold that the objections were not challenged, nor appealed against and that the patentee admitted that making the amendments "was a deliberate and conscious act".

Using this part of the file wrapper, the judge therefore construed the claims as being limited to that particular compound 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".

This case also looked briefly at the position of using the file wrapper in some other European jurisdictions (as defined by experts called by the UK Court).


German law is similar to the UK: the prosecution history is admissible as an aid to construction but reference to it is generally discouraged.


The French courts often refer to the file wrapper where interpretation of claims is required, and especially where the scope of protection has been narrowed to obtain grant of a patent. However, the claims must remain the source of the interpretation. The French courts put equal probative value on all documents from the file wrapper (be they letters from the examiner, statements by the patentee etc).


The Italian courts do not have a doctrine of file wrapper estoppel and that there is no clear rule of law as to the relevance of the file wrapper as an aid to the interpretation of the claims.


The Spanish courts will use file wrapper estoppel if the statements used are "unequivocal, clear, precise, conclusive, undoubted and [do] not reflect any kind of ambiguity". With regard to use of the estoppel with regard to claims expressly limited to overcome prior art, the Spanish courts "deem it a contradiction... [for an applicant] to have renounced a broader scope of protection during [prosecution] by introducing technical features which reduce the scope protected by its claims, and, subsequently, after the registration, to have attempted to broaden the scope of protection to include in its features that had been excluded from it by virtue of restrictions added by the applicant himself". This indicates that if the applicant restricts the claims during prosecution to overcome prior art, a broader interpretation of the claim cannot then be argued.


Although acknowledging the fact that courts should be cautious before relying on the file wrapper, Justice Arnold certainly put a lot of weight on the file wrapper when interpreting the claims in this case. It is difficult to decide whether this is a game changing decision or not. It is possible that the case may be appealed to the Court of Appeal and also, that the court acknowledges that in general, the application of file wrapper estoppel should be done cautiously by courts. However, it is worth noting the position of the court in this case and reminding ourselves that one should consider carefully amendments and statements made during the prosecution of a case as it may not be possible to broaden the interpretation later.

Further information

Full decision of Actavis UK Ltd (and Others) v Eli Lilly & Company, [2014] EWHC 1511 (Pat):