Not a Doctrine of Equivalents

We are often asked whether UK law recognizes a "Doctrine of Equivalents". The answer is that patent claims must be construed according to the Protocol on Interpretation of Article 69 of the European Patent Convention, which seeks to balance fair protection for the patentee with a reasonable degree of certainty for third parties. In applying the Protocol, the Courts of the United Kingdom have adopted a so-called purposive construction of claims, derived from a decision of the House of Lords (Catnic v Hill & Smith [1982] RPC 183) concerning a patent granted under the now-obsolete Patents Act 1949. In 1989, the Patents Court in Improver v Remington [1990] FSR181 reformulated the Catnic decision as three questions, and these three questions are now recognised as the standard for applying the Protocol. These questions, variously referred to as the "Catnic", "Improver" or "Protocol" questions are set out on below in a flow chart.

When using these questions, the Court is looking to see whether a variant on a feature specified in a claim falls within the scope of the claim. It might be thought that a variant would be expected to include equivalents. However, in practice, this does not appear to be the case. Indeed, the Courts are very careful not to use the term "equivalents", as this is not a doctrine by which the natural language can be ignored and something else can be substituted in its place. In Amersham Pharmacia Biotech v Amicon (unreported), Lord Justice Aldous stated “I do not believe that the Protocol introduced into our law a doctrine of infringement by equivalent effect by use of a different mechanism. That may be for the future.”