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File Wrapper Estoppel

Say what you mean, mean what you say

A patent application often describes how an invention differs from what has been done before, and sometimes sets out the key attributes that differentiate the invention from that prior art. When the application is examined, the applicant often goes further and in the arguments it presents to the patent office identifies features of the invention that it says are significant or critical.

After a patent has been granted, third parties need to be able to form a clear view of its scope, so that they can assess the validity of the patent and avoid infringement. Often, a review of the statements made in the specification and the arguments presented during prosecution of an application is helpful in determining exactly what the patent does and does not cover, but this form of interpretation can only be relied upon if the law imposes on the patent proprietor an obligation to abide by what it said in order to get the patent granted. Where that obligation does not exist, a patent applicant can say one thing in order to persuade the patent office to grant its application, but then something quite different when it seeks to enforce its patent against an alleged infringer.

In the USA, the doctrine of “file wrapper estoppel” is central to the assessment of the scope of a patent. By examining the correspondence between applicant and patent office examiner (which these days is usually freely available online), a third party can often identify statements that reveal the intended meaning of a patent claim and which prevent the patent owner asserting a broader claim scope in litigation.

In the UK, on the other hand, there is no equivalent judicial doctrine. Indeed, a senior judge has stated that “life is too short” for those considering the scope of a patent to have to consult the official file. Instead, the courts make up their own mind about the scope of the patent.

Now that the official files of all European patents and an increasing number of UK national patents are easily and freely accessible online, surely there is no reason why patent applicants should not be held to the statements they make in order to get their patents granted. Adoption of a strict file wrapper estoppel doctrine in the UK would provide much-needed certainty for those who seeking to avoid infringement.

What life is too short for is the sort of patent litigation that would never get off the ground if patent applicants were prevented from saying one thing about the scope of their claims to the patent office, but then something quite different to the courts.

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