In a recent patent case, Unwired Planet International Limited v Huawei Technologies Co Limited and others, the defendants tried to argue that a term used in the claims lacked clarity to the extent it was “truly ambiguous” and that as a result the patent in question was insufficient.

Importantly, in the UK, a patent can only be revoked on specific grounds. These grounds include any one of:

* the invention defined by the claims lack novelty,
* the invention defined by the claims lack inventiveness,
* the description provided of the invention lacks sufficiency.

However, curiously perhaps, this list does not include clarity. Therefore, according to the letter of law, although it is a requirement for grant, once granted, a patent cannot be revoked on the ground that its claims lack clarity.

On the face of it this puts potential patent infringers at a severe disadvantage – if the claims of a patent are unclear, then surely what a third party can do without risking infringement is also unclear. How can this be fair?

Well firstly, it should be noted that it seems well-established that if the scope of a claim is so completely unclear that it cannot be determined whether or not a product or process falls within its scope, then a court will normally conclude that, by definition it cannot be infringed (see for example Scanvaegt v Pelcombe).

Secondly, in Biogen v Medeva, the principle was established that if a claim is deemed “too wide”, that is, if it defines an invention in such a way that is disproportionately broad given the actual examples of the invention provided in the patent then this can render a patent insufficient. This is akin to a claim failing a clarity objection arguing that a claim is not supported by the accompanying description. The principle is sometimes referred to as “Biogen insufficiency”.

Thirdly, in a second well-known case, Kirin Amgen Inc v Hoechst Marion Roussel Ltd, a patent was revoked for lacking sufficiency because the claims were considered ambiguous. This ambiguity arose because the court found that the skilled person could not determine whether or not a particular product or process would fall within the scope of the claims. Importantly, this was not because the claims were incomprehensible - the skilled person could understand what the claims meant without undue burden. Instead the claims were considered ambiguous because to determine if a product or process fell within the scope of the claims required a technical test to be performed, and the court found the skilled person could not determine what this test was. It was reasoned therefore that the skilled person could never know if they were infringing the claims therefore the claims were “truly ambiguous”. As a result, the patent as a whole was deemed to lack sufficiency.

In Unwired Planet v Huawei Technologies, the patent related to a technique for converting certain values used by a processor of a mobile phone when it switches from 2G mode to 3G mode.

The defendants argued that the terms “converting” and “converted” used several times in the claims rendered the claims “truly ambiguous” and that the patent was insufficient. This was because, they argued, the skilled person would not be able to determine if they were performing a conversion within the meaning of these terms the claims. They argued that this was equivalent to the “truly ambiguous” claim from Kirin-Amgen case. On the facts, the judge disagreed and noted in particular that the claims in question do not set their scope based on the outcome of a particular test. The judge also noted that in cases where infringement can be shown – i.e. it can be demonstrated that at least certain products and processes fall within the scope of a claim, then any argument that the claims are truly ambiguous are “…likely to be met with scepticism”.

The judge also stated that just because a claim is difficult to construe this does not mean it is necessarily “truly ambiguous”. The judge also noted that the existence of a “fuzzy boundary” at the edge of a claim’s scope is not, of itself, objectionable.

The judge in the Unwired Planet case provided a succinct discussion on the UK law relating to clarity and sufficiency discussing in particular the relevant aspects of the Scanvaegt v Pelcombe, Biogen and Kirin-Amgen cases.

However, an observer might fairly conclude that there is still uncertainty about how a court will treat claims that are arguably unclear. In particular it still seems entirely possible that claims that quite clearly should have been rejected by the patent office as lacking clarity before grant will only be revoked by a court in quite narrow circumstances.

The advice to patent applicants is therefore to ensure that the claims of a patent application are as clear as possible, and certainly do not contain a fundamental defect that might leave them vulnerable to an attack on the ground that they are truly ambiguous.

On the other hand, for parties looking to attack a granted patent whilst it may be worthwhile to consider speculative attacks on the ground that the claims of a patent are unclear to the extent that they are insufficient, this should not be relied on and more traditional attacks on the grounds of lack of novelty and inventiveness should be considered first.