​On 30 November 2016 the European Patent Office’s Enlarged Board of Appeal appears to have finally resolved the longstanding legal uncertainty regarding ‘poisonous’ priority and divisionals by determining that partial priority provides an effective antidote.

The uncertainty related to situations where an inventor devises a particular invention, and then subsequently realizes that the particular invention may be extended to a broader scope that encompasses their first invention. Provided that a second patent application for the broader subject matter is filed within 12 months of a first patent application directed to the narrower invention, the second application may claim priority from the first application.

The claiming of priority enables the subject matter in the second application that is derived from the first application to be treated as if it had been filed at the same date as the earlier application, for the purpose of assessing whether the subject matter is novel and inventive. However, it was argued by some that, in this situation, separate publication of the content of the first application (e.g. in a divisional application) can be considered novelty destroying prior art with respect to the broader subject matter of the second application that was not, at least implicitly, disclosed in the first application. In this way, the content of the first application could be said to ‘poison’ the second application.

The Enlarged Board appears to have emphatically rejected these arguments, by publishing an order, on 30 November 2016, in relation to appeal case G1/15. The order states that priority applications cannot be used to destroy the novelty of the later application, when an effective claim to partial priority has been made. A formal decision of the case, which explains the Enlarged Board’s reasoning in detail, is expected shortly.

This is good news for patent owners and applicants because it removes concerns that filing a patent application at an early stage may prejudice the scope of protection that may ultimately be available, once an invention has matured into its broadest form. We generally recommend that our clients should aim to file patent applications at the earliest opportunity to avoid their commercial competitors securing an earlier filing date for the same, or similar, subject matter.