Since the introduction of the doctrine of equivalents in the United Kingdom in Actavis v Lilly, it has been questioned whether a claim can be extended by said doctrine (so that a product infringes the claim) where the product itself was obvious over the prior art at the priority date.
So far the English courts have recognised that, in such circumstances, a Formstein defence may be available (see Technetix v Teleste  EWHC 126 and E Mishan v Hozelock  EWHC 991 (Pat)); however, so far the issue has not needed to be decided. In Facebook v Voxer IP, the English Patents Court has again, orbiter, indicated the availability of such a defence.
Is such a defence needed?
The issue, to a degree, is one of public policy. Under English law, alternative solutions already exist. In particular, the Gillette principle says that a patentee cannot validly claim something which was not new or was obvious at the priority date. It follows that in a case in which the alleged infringement can be shown to be obvious over the prior art at the priority date, either the claims must not cover it as a matter of construction or they are invalid. The problem with this approach is that, if applied to the doctrine of equivalents, it may result in a finding that the patent is infringed but de facto invalid, not valid but not infringed. This approach could unduly deprive the patentee of its right.
Lord Justice Birss, giving judgment, put it as follows: “So imagine a case in which a claim on its normal construction is valid and not infringed, but a defendant’s device is (i) found to infringe by the doctrine of equivalents but also (ii) found to be obvious over the prior art. Is the right answer that the claim is infringed but invalid because its proper scope, taking into account equivalents, encompasses something obvious over the prior art; or is it 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? Either answer can be justified logically.”
What is a Formstein defence?
Formstein is a German case. As infringement and validity are bifurcated in German proceedings, the Gillette principle is not applicable when determining infringement (as it is directed to validity, not infringement). The conclusion was therefore that an alternative defence was available, namely that the claim was to be held to its normal construction (with equivalents not available) rather than being invalid. Lord Justice Birss explained: “[Formstein] is an extension of the Gillette defence to a case of equivalents so that if the … defence is made out, it leads to the conclusion that there is no scope for equivalents in the given circumstances and the patent’s scope must be held to its normal construction.”
What happened in the case at hand?
Voxer IP owned European Patent (UK) No. 2 393 259 for a method of transmitting voice and video data. It alleged that Facebook’s live broadcast feature infringed the patent. In response, Facebook commenced a revocation action before the English Patents Court, using the Shorter Trails Scheme. Voxer counterclaimed that the patent was infringed.
Infringement was advanced on a normal construction of the claims and on the basis of the doctrine of equivalents in two respects. Indirect infringement (means essential) was also alleged in certain respects. Facebook denied infringement and also alleged it had a Formstein defence.
The court concluded that the patent was obvious and, in any event, not infringed (either under a normal construction or the doctrine of equivalents). While the issue of the Formstein defence did not need to be decided, the court considered it nonetheless. The court held: “... if I did have to decide the matter, I would hold that the right approach is the Formstein approach so that the conclusion if the equivalent device lacks novelty or is obvious is that the claim scope must be confined to its normal construction in that respect. I would do so for two reasons. If the claim on its normal construction is valid, then it seems harsh to invalidate it on this ground. What else could the patentee do but write their claim in a way which, normally construed, did not cover the prior art. So that approach promotes certainty. Secondly, since it is clear that other EPC countries work that way, this is a reason in itself for this EPC state to take the same approach."