Historically, British courts had ruled that patent infringement was to be determined by a strictly literal reading of the patent claims. Patent claims are numbered paragraphs at the end of the patent that define the scope of the rights granted by the patent and specify technological solutions that should not be used without prior authorization. However, words are often imprecise and inadequate to describe complex technologies. For example, a minor change to the product could be deemed non-infringing as long as it fell outside the specific words of the claims. In recognition of the unfairness of this scenario, the courts created a doctrine of equivalents, which made it possible to hold a party liable for patent infringement even though the infringing product or process did not fall within the literal scope of a patent claim but nevertheless was equivalent to the claimed invention.
The doctrine of equivalents was generally recognized in the UK, but the test of equivalence established in 2005 was so stringent that it rendered the doctrine practically meaningless. The test required the courts to look at “what the person skilled in the art would have understood the patentee to be claiming.” Kirin-Amgen Inc v Hoechst Marion Roussel Ltd, 2005 RPC 9. A person of ordinary skill in the art looking at the words of the patent claims would usually interpret the words narrowly in a way that leaves little room for equivalents.
In July of 2017, the UK highest court revitalized the application of the doctrine of equivalents. Actavis UK Limited & Ors v Eli Lilly and Company, 2017 UKSC 48 (12 July 2017). To correct for the shortcomings of the prior test, Lord Neuberger, writing for the court in Actavis, established a two-prong test for patent infringement under the doctrine of equivalents: “… (i) does the variant infringe any of the claims as a matter of normal interpretation; and, if not, (ii) does the variant nonetheless infringe because it varies from the invention in a way or ways which is or are immaterial?” While the first prong of the test requires interpretation similar to the analysis under prior test, the second prong expands a court’s ability to analyze the materiality of the changes based on the facts and expert evidence.
The expansion of patent rights brings the UK law closer to the US law. U.S. Judge Learned Hand has described the purpose of the doctrine as to “prevent an infringer from stealing the benefit of the invention.” Royal Typewriter Co. v. Remington Rand, Inc., 168 F.2d 691, 692 (2d Cir. 1948). In the U.S., the courts consider whether “the accused product performs substantially the same function in substantially the same way with substantially the same result as each claim limitation of the patented product.” Warner-Jenkinson Company, Inc. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997). While not perfect for chemical cases (for example, aspirin and ibuprofen are equivalent under this test as discussed by the Federal Circuit), the test strives to promote fairness and innovation. This test has restored power to the doctrine of equivalents in the UK and is a welcome development for patent owners.