9.3.2 Relationship between invalidity and infringement proceedings
U.K. courts do not generally bifurcate the determination of the issues of patent infringement and validity; the issues are heard together. Consequently, a patentee cannot attempt to apply a different, narrower interpretation of the patent and its scope when the court is considering the issue of validity and an expansive interpretation when considering the issue of infringement. As it was once said by Lord Justice Jacob in the Court of Appeal:
Professor Mario Franzosi likens a patentee to an Angora cat. When validity is challenged, the patentee says his patent is very small: the cat with its fur smoothed down, cuddly and sleepy. But when the patentee goes on the attack, the fur bristles, the cat is twice the size with teeth bared and eyes ablaze.61
This also gives rise to so-called squeezes on the patentee, such as where the claimant contends that, if the claim is construed widely enough to cover the defendant’s product, then it is also wide enough to cover the prior art and so must, accordingly, be invalid. Alternatively, if it is construed narrowly enough to avoid the prior art, then it does not cover the defendant’s product, and so there can be no infringement.