Lord Justice Birss (sitting as a High Court judge) has said that he considers that the correct way to deal with a successful application of the Formstein defence would be to hold a patent's claims to be valid but not infringed, rather than infringed but invalid.
Such an approach would help to avoid a harsh result for patentees, promote certainty and maintain consistency with other European Patent Convention states. Although obiter, Birss LJ's comments are indicative of the likely approach the UK court will adopt should the Formstein defence need to be applied.
The judgment concerned a revocation action brought by Facebook Ireland Limited against Voxer IP LLC as part of a multi-jurisdictional dispute. In return, Voxer alleged that certain features provided by Facebook on certain apps, known as Facebook Live and Instagram Live, infringed its patent EP (UK) 2 393 259. The dispute has proceeded via the Short Trial Scheme and has already provided useful guidance on how the doctrine of equivalents should be pleaded in patent cases (see our earlier Insight).
Birss LJ concluded that Voxer's patent was not infringed by any of Facebook or Instagram's live features and also that the patent in suit was invalid for obviousness over a prior art citation.
The Formstein defence
The UK Supreme Court explained how the doctrine of equivalents should be applied under UK law in Actavis v Eli Lilly  UKSC 48. A number of questions arose as a result of this decision including, because Actavis only considered infringement, whether and how the doctrine of equivalents should be applied to invalidity arguments.
The Formstein defence is effectively an application of the well-established Gillette principle, extending it to the doctrine of equivalents. In a Gillette defence, the alleged infringer argues that what they were doing would have lacked novelty or have been obvious at the relevant patent's priority date, such that if the patent was valid it could not be infringed. Formstein was a German case in which equivalents were considered by the infringement court which held the patent's claim to its normal construction rather than being invalid.
As Birss LJ explained at paragraph 211 of the decision, it the court decides a patent is valid but not infringed on its normal construction, it must then go on to consider infringement by equivalents. What is the solution if the defendant's device is found to infringe by equivalents, but it is also found to be obvious over the prior art? The UK courts have previously recognised this dilemma but also possibility of the Formstein defence existing in English law (for example, in Technetix v Teleste  EWHC 126 and E Mishan v Hozelock  EWHC 991). However, no case has yet arisen which in which the UK court has needed to apply the defence, and nor has it been clear how such a defence would operate.
Despite not needing to decide the issue, Birss LJ elected to provide guidance. He summarised the predicament, asking whether as a result the claim should be "infringed but invalid because its proper scope, taking to account equivalents, encompasses something obvious other the prior art" or "valid but not infringed on the footing that part of the law of equivalents mandates that if these are the facts the equivalents doctrine does not expand the claim?".
In Birss LJ's view, either answer could be justified logically. However, he considered that the right approach – if the device infringed by equivalents but, as a consequence, either the claim lacked novelty or was obvious – was to confine the claim to its normal construction. This would lead to a claim being valid but not infringed on the basis that it (i) would be harsh to invalidate a claim that was valid on a normal construction, and (ii) promoted certainty as a patentee could only write its claims such that they didn't cover the prior art on a normal construction (the first point effectively being a consequence of the second). This approach in Formstein itself (which, due to the bifurcated German court system, did not have jurisdiction to invalidate the claim) to uphold the patent's validity, but restrict it to a normal construction that wasn't then infringed, has also been followed in the Netherlands and the US.
This decision provides another example that the UK courts are likely to accept the Formstein defence when required. However, Birss LJ has now gone one step further than previous decisions, providing his views on how the defence would apply in practice. Although not binding on the High Court, coming from such an experienced and well-regarded intellectual property judge who now sits on the Court of Appeal, it provides a strong indication of the approach the UK courts are likely to adopt.