Is purposive construction set to change?

PLG Research Limited v Ardon International Limited

Author: David Rickard, Partner, Boult Wade Tennant

Change is in the wind, or is it? The Court of appeal in PLG Research Limited -v- Ardon International Limited, in a judgment of the Court, delivered on 16 November 1994, signalled a possible intention to change the previously well established test of claim construction set down by Lord Diplock¹ in Catnic Components Limited -v- Hill and Smith Limited.

The Court was careful to state that it did not need to make reference to the Catnic test because the question to be determined was whether the starting material was "substantially uniplanar". It did not decide that the Catnic approach is different to the approach laid down by the Protocol on interpretation under the European Patent Convention ("EPC"). However, the Court did suggest that there could be a difference between the two approaches and made various comments of note.

Background
The UK approach to construction of claims under the 1949 Patents Act was stated by Lord Diplock in Catnic and has become known as the "Purposive Construction" test. Catnic was decided in 1980. Mr Justice Hoffman, as he then was, in Improver Corporation -v- Remington Consumer Products Limited² analysed Catnic as requiring the Court to ask three questions, namely:

(1) Does the variant have a material effect upon the way the invention works? If yes, the variant is outside the claim. If no -

(2) Would this have been obvious at the date of publication of the patent to a reader skilled in the art? If no, the variant is outside the claim. If yes -

(3) Would the reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention? If yes, the variant is outside the claim.

In Improver³, Lord Justice Dillon stated that Lord Diplock's speech in Catnic indicated the same approach to construction as that required by the Protocol on interpretation to Article 69 of the EPC. Lord Justice Dillon's statement was made at the interlocutory stage of the case and Hoffman J regarded it as binding on him at the trial. It has since been assumed in a number of cases including Southco Inc v Dzus⁴ that the "Purposive Construction" test propounded by Lord Diplock is in accordance with Article 69 EPC and the Protocol relating thereto, which must be applied in the UK (S125(3) Patents Act 1977). In the result the patent in suit in Improver was held not to be infringed, although in similar litigation elsewhere in Europe concerning the same patent and the same disputed device the opposite conclusion was reached and the patent was held to be infringed. In fact, the German Court expressly rejected the conclusion of the English Court, commenting that the English Court's finding was probably the result of applying the Catnic test of construction which related to the law prior to the EPC.