The Doctrine of Equivalents – where are we now?
Since July 2017 and the Supreme Court judgment in Actavis v Eli Lilly, the UK has had a doctrine of equivalents as part of its law on patent infringement

In this article, we look again at the impact that this has had on our courts and the cases before them. In a world where everyone loves data and statistics, we have attempted to distil the wealth of UK case law on this doctrine into a few easy-to-digest graphs. We analyse the number and proportion of patent infringement judgments in which an argument of infringement by equivalence has been advanced at trial; the areas of technology involved in those judgments; the number of judgments in which infringement by equivalence was found; and how often patent prosecution history has been relied on to try and avoid a finding of infringement by equivalence, taking into account the judgments handed down to date. We also comment on some recent UK case law concerning the doctrine of equivalents. Finally, we address recent changes to EPO practice concerning description amendments and their potential impact on findings of infringement by equivalence.

To conduct this analysis, we have reviewed the patent infringement judgments handed down each year from 2017 (post-Actavis) to date (which we have called “Infringement Judgments”) and identified in which of those judgments infringement under the doctrine of equivalents was in issue (which we have called “DoE Judgments”).[1]

Proportion of Infringement Judgments arguing the DoE

Between 2018 and 2020, the proportion of all Infringement Judgments in which infringement by equivalence was in issue increased year-on-year, as shown in Figures 1 and 2 below, reaching a peak of 90% in 2020.  However, 2021 may mark the end of this trend:  As of October 2021, out of 17 Infringement Judgments handed down this year, we have identified just 7 DoE Judgments,[2] representing 41% of the 2021 Infringement Judgments handed down.

Figure 1: Chart showing the number of DoE Judgments (shown in pink), compared to the total number of Infringement Judgments (shown in pink and blue) per year, from 13/07/2017 – 26/10/2021

Figure 2: Chart showing the number of DoE Judgments as a percentage of Infringement Judgments, by year, from 13/07/2017 – 26/10/2021

DoE Judgments where infringement by equivalence has been successfully argued

 In 2021, infringement by equivalence was found in 3 of the 7 DoE Judgments, representing a success rate of 43%.[3]  The argument appears to have been less successful in 2021, as compared to earlier years (see Figure 3 below).  Of particular note is that in 2019, infringement by equivalence was found in every one of the 7 DoE Judgments (i.e. a success rate of 100%).

The year-on-year trends can be seen in Figure 3 below, which shows the number of DoE Judgments per year (whole bar), and the number of these cases in which infringement by equivalence was actually found (pink portion of bar).  Taking all of the post-Actavis DoE Judgments to date, the doctrine has been successfully argued in 16 out of 26 cases (62%).  However, as will be explored further below, in the majority of cases where infringement by equivalence was found, the case did not turn on this point (either because infringement under a normal claim interpretation was found, or because the patent was held invalid).

Figure 3: Chart showing the number of DoE Judgments and the number of cases in which a finding of infringement under the DoE was found, from 13/07/2017 – 26/10/2021.  The percentages above each bar show the success rate of the doctrine of equivalents in each year.

DoE Judgments turning on a finding of equivalence

So far in 2021, as noted above, a finding of infringement by equivalence was made in 3 of the 7 DoE Judgments.  In all 3 of these cases, the patent was found valid.[4] However, only 2 of these cases[5] actually turned on the finding of infringement by equivalence as, in the other, infringement was also found on a normal claim interpretation (i.e. the primary meaning of a claim, with no consideration of the doctrine of equivalents).[6]

Taking into consideration all DoE Judgments handed down from 2017 to 2021, only 23% of DoE Judgments have actually turned on a finding of infringement by equivalence, as shown in Figure 4 below.  This may be a contributing factor to the apparent recent decline in popularity of the argument.

Figure 4: Chart showing the number of DoE Judgments which have turned on a finding of equivalence (as at 26/10/2021)

Areas of technology where infringement by equivalence has been argued

The following chart shows the different areas in which infringement by equivalence has been argued to date (as identified from the IPC classes of the patents in dispute).

While pharmaceutical and chemical patents in the life sciences sector dominate, the UK courts have seen cases covering technologies including construction, engineering and electronics. Two recent additions are actions covering “wearing apparel” (A41)[7] and “aircraft, aviation and cosmonautics” (B64),[8] both relating to judgments handed down in 2020, demonstrating that the doctrine of equivalents is being argued across a wide range of technologies.


Figure 5: Chart showing the distribution of IPC codes in the DoE Judgments so far (as at 26/10/2021)

Prosecution history

In Actavis, the Supreme Court commented on the relevance of the patent prosecution history in the assessment of claim scope. As a reminder, the UK courts have typically discouraged looking at the contents of prosecution files for the purposes of determining claim scope and have rarely done so.  Lord Neuberger clarified in Actavis that the two situations where it would be appropriate to do so are:

  • if the point at issue is unclear based on the specification, and the file unambiguously resolves the point; or
  • if it would be contrary to the public interest to ignore the file, e.g. where a patentee has stated previously that it would not enforce the patent against a particular variant.

Figure 6: Chart showing the number of DoE Judgments where prosecution history has been argued so far (as at 26/10/2021).

As shown in Figure 6 above, defendants have only attempted to rely on the prosecution history in a minority of DoE Judgments – only 6 of the 26 DoE Judgments since Actavis have discussed prosecution history. Notably, in none of those cases has prosecution history been successfully used to defend an infringement by equivalence claim.


Recent UK case law on the doctrine of equivalents

 Inventive concept

 The first Actavis question (Actavis v Eli Lilly) asks whether the variant in issue achieves “substantially the same result in substantially the same way as the invention, ie the inventive concept revealed by the patent.”  In characterising the first Actavis question in this way, the Supreme Court reduced the importance of the language of the claims to determine the scope of protection, and raised the significance of the inventive concept – a change in approach from previous case law.

Little guidance was given by the Supreme Court in Actavis on how parties should determine the inventive concept and hence, unsurprisingly, much of the post-Actavis case law has centred on its characterisation (see. for example, our article from 2018 on Icescape Ltd v Ice-World International BV in which the Court of Appeal provided useful guidance on this point).  Patentees typically seek to argue an inventive concept with a higher level of generality in an attempt to achieve a greater scope of protection, while defendants typically seek to characterise the invention more narrowly.  This is a question of interpretation and has resulted in less certainty for both patentees and third parties.

Some further guidance has been given in recent case law. In Kwikbolt v Airbus [2021] EWHC 732 (IPEC), HHJ Hacon defined the inventive concept as “the new technical insight revealed by the invention as claimed, in the context of the specification as a whole, as it would have been perceived by the skilled person at the priority date”, which will be influenced by the common general knowledge.  He also made clear that the skilled person must arrive at their assessment of the inventive concept without the variant in mind.  In Insulet v Roche [2021] EWHC 1933 (Pat), Deputy Judge Pat Treacy considered that both the technical result, and the means used to achieve it, are part of the inventive concept.  In IPCom v Vodafone [2020] EWHC 132 (Pat), Mr Recorder Douglas Campbell QC used the same characterisation of the inventive concept for both the infringement analysis under the doctrine of equivalents, and the obviousness analysis, suggesting that the approach to be taken is the same when considering both infringement and validity.

Strict compliance

The third limb of the Actavis test asks whether the skilled person would have understood that strict compliance with the primary meaning of the claim was an essential requirement of the invention. In IPCom v Vodafone [2021] EWCA Civ 205, the Court of Appeal considered that, in making his or her assessment, the skilled person would be deemed to know that a claim had been amended so as to ensure its validity.  Interestingly this was not considered to be the case at first instance – Mr Recorder Douglas Campbell QC had considered that the skilled person would not know of such amendments, particularly in view of the fact that under s.27(2) Patents Act 1977, “An amendment of a specification of a patent … shall have effect and be deemed always to have had effect from the grant of the patent”.  In both cases, however, the Court held that the answer to the third Actavis question was “no” and hence infringement by equivalence was found in each instance.

Additionally, the UK courts continue to explore the possibility of a Formstein-type defence existing in UK law.  This issue was considered recently by Birss LJ, sitting down from the Court of Appeal, in Facebook v Voxer [2021] EWHC 1377 (Pat).  Although on the facts of the case he did not have to resolve the issue, Birss LJ considered, obiter, that where a claim is found to be infringed under the doctrine of equivalents but, as a result would be invalid for lack of novelty or obviousness, the claim should be held to be valid, but not infringed by the variant.  Birss LJ considered that this was the fairest approach for patentees, whose claims would not be found to be invalid on a normal construction, and noted that other EPC countries apply the law in the same way.  Although not binding, Birss LJ’s comments may give an indication of things to come, particularly given his wealth of experience in the Patents Court and his appointment to the Court of Appeal.

On a more practical level, Birss LJ recently made clear in the pre-trial review judgment in Facebook v Voxer ([2021] EWHC 657 (Pat)) that an argument of infringement based on the doctrine of equivalents must be referred to in the Particulars of Infringement.  At a minimum, Birss LJ noted that the Particulars of Infringement must “contain a statement, by reference to each relevant claim feature (and claim), that equivalence is relied on“.  However, Birss LJ noted, obiter, that it was probably not necessary for all of the details to be characterised at the outset, or for the inventive concept to be characterised in the pleadings.  Birss LJ noted that the cases in the IPEC would likely require the latter point to be pleaded, echoing the sentiments of HHJ Hacon in Kwikbolt v Airbus [2018] EWHC 2450 (IPEC).  Patentees must therefore, at a very early stage of proceedings, carefully consider whether or not a doctrine of equivalents argument could be run, or risk this argument being struck out.

Disclosed but not claimed is disclaimed

In Akebia v Fibrogen [2020] EWHC 866 (Pat), Arnold LJ, following a German decision,[9] held that where embodiments of an invention are disclosed but not subsequently claimed, they should not be considered to be encompassed by the claims, on either a literal or equivalence basis.  This has sometimes been referred to as the “disclosed but not claimed is disclaimed” principle, and has been referred to in many jurisdictions, including the US and the Netherlands.  Arnold LJ also referred to another German decision: Case X ZR 69/10 – Diglycidverbindung (Diglycidyl Compound) (September 2011).  This case noted that it must be determined whether the potentially infringing variant has more in common with the claimed solution or the solutions disclosed in the description of the patent in suit (but not claimed). In the latter case, infringement under the doctrine of equivalents is excluded.  The decision of Arnold LJ in Akebia has been recently overturned by the Court of Appeal[10] but the decision on equivalence was not appealed.

Similarly, at paragraph 72 of Actavis, there was a suggestion that if other pemetrexed salts were disclosed, but only the disodium salt was claimed, this would imply that the patentee intended other pemetrexed salts to be excluded and infringement by equivalence would not be found.  In actual fact, only pemetrexed sodium, and the broader class of “anti-folates” was disclosed in the specification.

New EPO guidance on embodiments that are not claimed

EPO guidance has long stated that inconsistencies between the description and the claims should be avoided.  However, in March 2021, the EPO published new, stricter guidelines, noting that embodiments in the description that are not covered by the claims must be deleted, unless they can “reasonably be considered to be useful in highlighting specific aspects of the amended claims”, or it is “prominently stated” that the embodiment is not part of the invention.

However, a patent that “prominently” states that a particular embodiment is not part of the invention is likely to pose problems if the patentee later wishes to argue that such an embodiment (or a similar embodiment) infringes the patent under the doctrine of equivalents, particularly when assessing the third limb of the Actavis test.  Patentees may therefore wish to consider whether to instead delete the unclaimed embodiments in their entirety, whilst making sure to include an underlying general disclosure in the specification (e.g. the general class of “anti-folates” in Actavis) to avoid unintentionally constraining claim scope.



Following our review of the recent UK judgments in which a doctrine of equivalents argument was advanced, we have identified some key themes:

  • The number and proportion of DoE Judgments has increased over the past few years, but appears to have reduced over the course of 2021
  • The doctrine of equivalents is being pleaded in patent infringement cases covering a broad and expanding range of areas of technology. Life sciences continue to dominate but the doctrine has been applied to diverse areas, such as “wearing apparel” and “aircraft, aviation and cosmonautics”
  • While parties in 6 DoE Judgments post-Actavis have sought to rely on the patent prosecution history, we have identified no instances where the prosecution history was successfully used to defend an infringement claim, and this point appears to have all but stopped appearing in doctrine of equivalents judgments

We have done our best to gather this data from public sources and analyse the ever-changing application of this doctrine. We last did this exercise back in 2020 and the eagle-eyed amongst you will spot that we have updated our methodology since then. We will aim to keep improving on this and will let you have our further observations in due course.


[1] All information has been obtained from publicly available judgments and not from an analysis of the pleadings. We have included cases from the IPEC, Patents Court, Court of Appeal and the Supreme Court. For completeness, we note that in calculating the number of Infringement Judgments, we have only included final judgments (i.e. not interim decisions), and only those judgments in which infringement was in issue.  We have not included cases where infringement was admitted (and therefore where it is unclear from the judgement on what basis infringement was argued). Where a case has been appealed, we have included both the first instance and appeal decisions in the statistics, but only where infringement was also in issue on appeal.  When calculating the number of DoE Judgments, we have included all cases where a party is said to have run an argument under the doctrine, even if this was not considered by the Judge (e.g. because the patent was held to be invalid).

[2] Illumina v Latvia MGI [2021] EWHC 57 (Pat), IPCom v Vodafone [2021] EWCA Civ 205, Kwikbolt v Airbus [2021] EWHC 732 (IPEC), Facebook v Voxer [2021] EWHC 1377 (Pat), ADD2 v DSPACE [2021] EWHC 1630 (Pat), Insulet v Roche [2021] EWHC 1933 (Pat), A Ward Attachments v Fabcon Engineering [2021] EWHC 2145 (IPEC).

[3] IPCom v Vodafone [2020] EWHC 132 (Pat), Illumina v MGI [2021] EWHC 57 (Pat) and A Ward Attachments v Fabcon Engineering [2021] EWHC 2145 (IPEC).

[4] For completeness, we note that in A Ward Attachments v Fabcon Engineering [2021] EWHC 2145 (IPEC), only the parent patent was held to be valid and a divisional was revoked for added matter over the parent patent.  In Illumina v Latvia MGI [2021] EWHC 57 (Pat), 4 patents were held to be valid but 1 was revoked for obviousness.

[5] IPCom v Vodafone [2020] EWHC 132 (Pat); A Ward Attachments v Fabcon Engineering [2021] EWHC 2145 (IPEC).

[6] Illumina v Latvia MGI [2021] EWHC 57 (Pat)

[7] Freddy Spa v Hugz Clothing [2020] EWHC 3032 (IPEC)

[8] Lufthansa v Astronics [2020] EWHC 1968 (Pat)

[9] Case X ZR 16/09 – Okklusionsvorrichtung (Occlusion Device)

[10] [2021] EWCA Civ 1279