Patents: possible defence to infringement by equivalence

By Audrey Horton



The Intellectual Property Enterprise Court (IPEC) has held that a patent was invalid but also considered a possible defence to infringement by equivalence.


A patentee should not be able to prevent a person from doing what they had lawfully been entitled to do before the patent was granted (the Merrell Dow principle) (Merrell Dow Pharmaceutical Inc v HN Norton & Co Ltd, 

Where an alleged infringement differs in only a non-novel or non-obvious way from the prior art at the priority date of the patent, the defendant has a good defence to infringement (Gillette defence) and it is not necessary also to challenge the validity of the patent (Gillette Safety Razor Co v Anglo-American Trading Co Ltd [1913] 30 RPC 465).

The scope of patent claims is determined in accordance with Article 69 of the European Patent Convention and the Protocol on the Interpretation of Article 69, which aim to provide a balance between fairness to the patentee and giving the public reasonable certainty as to what those claims cover.

In Improver v Remington, the High Court set out a three-step test for determining whether variation from the exact claim language falls within the scope of the claim (the Improver questions) ([1989] 5 WLUK 162).

In Actavis UK Ltd v Eli Lilly and Co, the Supreme Court considered the scope of protection of a patent claim when assessing infringement, and reformulated the law (the Improver questions) relating to infringement by immaterial variants ([2017] UKSC 48).


The owner, TN, of a patent for a component in a cable TV or broadband system sued TL for patent infringement by marketing equipment used to transmit cable TV or internet signals. TL counterclaimed to revoke the patent because of alleged lack of novelty and inventive step. 

TN applied to amend the patent, and accepted that, if claim 1  was invalid over the cited prior art, none of the other claims were valid. 

TL argued that, if its product fell within the scope of claim 1, it had a defence to infringement if the product lacked novelty or inventive step over the prior art.


The IPEC held that the patent was invalid. The TL product was found to fall outside the patent claims according to normal interpretation rules but within the claims under the doctrine of equivalents.  The IPEC also made obiter comments on a possible defence to infringement by equivalence. 

Before Actavis, the Merrell Dow principle was reconciled with the law on the construction and infringement of patent claims by the availability of the Gillette defence. It would be surprising if the Supreme Court in Actavis had intended to abandon the Merrell Dow principle without expressly saying so.

The issue raised in this case was the relationship between the scope of a claim and prior art which would invalidate the claim, taking into account both novelty and inventive step.

One way of reconciling the Merrell Dow principle with the doctrine of equivalents would be to say that if an accused product or process was an equivalent and for that reason was nominally within the scope of the claim, but the equivalent would have lacked novelty or inventive step over the prior art at the priority date, then it was deemed to fall outside the scope of the claim, so providing a defence to infringement. German law provided

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