In our Information Letter N.S.180 we reported on an Appeal Board decision in the case of Snack Food/Howard which set out a fairly liberal test for determining whether or not a patent claim was entitled to a priority date based on an application from which convention priority had been claimed. Essentially that decision held that simply because a claim was more limited than the disclosure of the application from which priority was claimed did not necessarily mean that convention priority was lost.

The issue has now come before the Enlarged Board of Appeals in a case in which the President of the EPO used his power to refer questions of law to the Enlarged Board for a ruling.

The basic requirement of the European Patent Convention for a valid claim to priority is whether the claim in question is for the "same invention" as that which was described in the application from which priority was claimed. After considering a number of situations in which anything other than a strict interpretation of this requirement might prejudice third parties, the Enlarged Board concluded:

Thus the test as to whether a claim is entitled to priority will henceforth be similar to that which is applied in determining whether a proposed claim amendment is permissible or not in the light of the original disclosure. Of course, one is allowed include in a European application as filed claims which do not meet these criteria. However, such claims will not be entitled to any date earlier than the date of filing of the European application itself. It is therefore desirable when filing one's original application to make sure that one has provided proper support for anything that one might subsequently wish to claim in the European application. In this context it should be recalled that it is possible to claim priority from multiple applications so that if one's concept of the invention develops after the filing of the first application for it, it may be prudent to file further applications to take account of such developments so that claims may be based on the subject matter of such further applications. At least in principle, Article 88(2) provides for the possibility of a single claim having more than one priority date.