Summary and implications

The English Patents Court has just handed down a significant judgment that determines the priority date that should be given to a patent.1 This is important because it will determine the relevant prior art that can be deployed against the patent, with potentially dramatic results in fields where there is rapid technical change – life sciences and high-technology in particular.

We expect that:

  • Great attention will now be given to patents that may be susceptible to priority attacks, as this can radically broaden the available prior art to the detriment of the patent in question. In practice there are likely to be many granted patents where the patentee's approach has been to get in the priority rights after filing, rather than beforehand.
  • As this priority issue is binary, the Patents Court will readily strike down a claim to an earlier priority date if there is no clear entitlement to it.
  • Extra attention will now need to be given to potential priority issues in corporate and licensing transactions. This may have consequences on indemnities, warranties, and on valuations.


This issue arose in the context of litigation between Edwards Lifesciences and Cook Biotech on the revocation of a patent for Cook's artificial heart valve. The disputed claim to priority was a matter of importance because, if priority was lost, a particularly significant scientific paper published between the original US priority application and the later PCT international application became relevant prior art.

The original US application was filed in the names of three individuals, all as joint inventors. Only one of these was an employee of Cook at the time the invention was made. The others were not.

The later PCT application was filed in the name of Cook, but when filed the only interest Cook had in the invention was as the employer of one of the three co-inventors. The other two inventors subsequently assigned

their rights to Cook nearly two years later; this was after the PCT had been filed but before grant of the litigated patent.

The decision

This kind of priority dispute is an unusual one, and depends upon the correct interpretation of Article 4 of the Paris Convention (Stockholm revision). This specifies that a person is to enjoy a right of priority if he has filed a relevant application for a patent or if he is the successor in title to such a person (i.e. in the context of a patent this must mean successor in title to the invention).

Cook argued that its claim to priority was a good one because (i) it had acquired all rights in the invention before the relevant patent was granted, and (ii) it had in any event always owned a third of the rights through its employee as one of the co-inventors.

Edwards argued that this was incorrect because the right of priority may only be enjoyed by the person who filed the priority application or his successor in title as at the date the right to priority is claimed. Because on the relevant date that was Cook jointly with the two individuals and not Cook alone, Cook was not entitled to the whole right to priority.

The Patents Court held that the effect of Article 4 was clear.

  • A person who files a patent application for an invention can claim priority only if he himself filed the earlier application from which priority is claimed, or if he is the successor in title to the person who filed that earlier application. If he is neither of these then he cannot claim priority.
  • Moreover, his position is not improved if he subsequently acquires title to the invention. It remains the case that he was not entitled to the right to priority when he filed the later application. Any other interpretation would introduce uncertainty and the risk of unfairness to third parties.
  • The alternative argument run by Cook was that it always owned its employee's interest in the invention and that was sufficient. As the US application was filed in the names of the three joint inventors, it was not filed by the employee alone and therefore he was not "a person" who had "duly filed an application for a patent" within the meaning of Article 4A(1). The Patents Court therefore held that the patent was not entitled to the earlier priority. The result was therefore that the potentially important scientific paper became materially relevant, and indeed was one of the pieces of prior art against which the patent was held to be obvious.

Further points

It should be noted that the EPO Board of Appeal has adopted the same approach to the interpretation of Article 87 EPC in two cases: J 0019/87 and T 0062/05.

The Patents Court's approach on Cook's alternative argument (employee-based ownership of an interest) is consistent with the EPO Board of Appeal in case T 0788/05.