03 April 2019 | Audrey Horton Professional Support Lawyer


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, www.practicallaw.com/9-100-0033). 

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 for such a defence (the Formstein defence), as did Dutch law. The US had a similar principle called ensnarement: the range of equivalents could not be so extended as to ensnare the prior art. It was possible that the Court of Appeal or the Supreme Court might introduce a Formstein defence into English law, considering the interplay between the scope of a claim on the one hand and novelty and inventive step on the other.

To establish infringement, as explained in Actavis, a patentee had to show that the accused product or process either had all the integers of the claim on a normal construction or, taking all the equivalent features of the accused product or process in sum, that it satisfied the three revised Improver questions. A patentee did not always have to go through each integer of his claim and the corresponding features of the accused product or process, and wherever an integer of the claim was missing from the accused product or process, identify its equivalent. The Improver questions addressed the variant product or process as a whole. All integers of a claim missing from the variant would be relevant to, for instance, whether the inventive concept had been exploited by the variant in substantially the same way to achieve substantially the same result. No integer could be ignored. But since it was the variant as a whole that was considered, a patentee was not invariably required expressly to assert equivalence in relation to each integer of the claim, one by one. An accurate identification of the inventive concept might be enough to focus attention on the integers that mattered.

Characterising the inventive concept or core accurately was important to the scope of a claim. From a patentee's perspective, the simpler the inventive concept, the more likely it was that the concept had been exploited in substantially the same way to achieve substantially the same result. From an alleged infringer's point of view, the more detailed the inventive concept, the less likely it was that the concept had been so exploited.

The finding that the TL device fell within the scope of claim 1 under the doctrine of equivalents demonstrates how a Formstein defence, if it existed in UK law, would limit the scope of infringement by equivalence. The TL device fell within claim 1 partly because the inventive concept was relatively simple. Where, as here, the simplicity of the inventive concept or core tended to make the scope of the claim broader, this would also increase the likelihood that a Formstein defence would apply.


Although the IPEC's comments were obiter, the Formstein defence was fully pleaded and argued at trial. It was considered highly significant that the patent courts of other countries, which also have a doctrine of equivalents, at the same time assess the expanded claim scope from the validity standpoint and in appropriate cases allow a Formstein defence.  The reasoned decision that TL was entitled to the defence may indicate the continued direction of travel of the courts in seeking to restrain the doctrine of equivalents. Whether the defence, which can provide a route for a party found to infringe by equivalents to escape liability, applies in UK law after Actavis is likely to be appealed to the Court of Appeal and ultimately to the Supreme Court. 

Case: Technetix BV & Ors v Teleste Ltd [2019] EWHC 126 (IPEC).

First published in the April 2019 issue of PLC Magazine and reproduced with the kind permission of the publishers. Subscription enquiries 020 7202 1200.


About the Author

audrey horton module

Audrey Horton
Professional Support Lawyer
As the knowledge and development lawyer in our Intellectual Property Group based in London, I play a key part keeping the IP team up to date with legal developments and case law, scanning the horizon to ensure we are at the forefront of new trends.

Direct: +44 (0)20 7415 6000

[email protected]

You may also be interested in