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  • Writer's pictureRosie Burbidge

What is the test for patent infringement in the UK?

We don’t tend to cover patent cases on this blog, but a recent judgment of Mr Justice Zacaroli highlights some important points about the test for patent infringement in the UK, which has become more complicated in the past few years.

The case, Noblelight Ltd v First Light Lamps Ltd, concerned technology used in arc lamps. The invention related to an improvement to the beads used to seal the glass tubes in the lamps. The size of the bead used was critical to the argument about infringement.

In his judgment, Zacaroli J found the patent to be valid. He also found that the defendant’s method for sealing the ends of lamps infringed the patent on a purposive construction and by equivalents, but not literally.


Noting that the patent in question was a method patent, not a product patent, the judge concluded that, on a purposive construction:

“the protection sought in the Patent is not limited to a method in which beads are precisely no bigger than the outer diameter of the tube, but include variants in which the bead is not materially bigger than the outside diameter of the tube to an extent ‘which could have no material effect upon the way in which the invention worked’” (quoting Lord Diplock’s judgment in Catnic).

The judge found that in this case there was no material difference between infringement based on purposive construction and infringement by equivalents.

Applying the questions set out by the Supreme Court in Actavis on infringement by equivalents, Zacaroli J found that the variant achieved substantially the same result in the same way. It would not be obvious to the skilled person that it did so; and a reader of the patent would not have concluded that strict compliance with the literal meaning was intended.

However, he rejected the case based on literal infringement, which depended on one lamp manufactured using a bead that was no bigger than the outer diameter of the tube. The judge was not satisfied that this sample amounted to literal infringement or that it occurred on a more than de minimis basis, as it could be attributed to human error. “This is an insufficient basis, in my judgment, for concluding that First Light makes lamps using beads that are no bigger than the outer diameter of the tube on any more than a de minimis basis,” he said.


First Light challenged the validity of the patent on the ground that it did not involve an inventive step over two pre-existing patents. But the judge essentially found that these identified different solutions to the same problem and therefore the skilled person would not regard the patent as being obvious over them.

What does this mean?

Following recent cases including the landmark Actavis judgment, the question of patent infringement has become more complex in the UK. As this case shows, the judge may have to assess literal infringement, infringement based on purposive construction of the claims and infringement by equivalents. Each of these assessments involve different considerations and may result in different findings (as in this case).

This also means parties in patent cases – both claimants and defendants – need to evaluate the strength of the infringement case based on the different tests and ensure they have sufficient supporting evidence.

To find out more about the issues raised in this blog contact Rosie Burbidge, Intellectual Property Partner at Gunnercooke LLP in London -

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