Priority claims are reviewed in a United Kingdom patent court, with potential negative impact for companies who are not named in initial applications.

In a recent case before the United Kingdom patent court, Edwards Lifesciences LG v Cook Biotech Incorporated [2009] EWHC 1304 (Pat), the issue of a valid priority claim was explored, particularly in the circumstance of the applicant of the earlier application being different to the applicant of the later application claiming priority. This highlights the risk of US practitioners dealing with assignments from the inventors after the end of the priority year in cases where overseas filings (outside the United States) are desired.


This case related to a granted European patent which was initially filed as a PCT application in the name of Cook Biotech Incorporated (Cook), the PCT claiming priority from an earlier US application. The earlier application was filed in the name of the joint inventors: Joe Obermiller, Francisco Osse and Patricia Thorpe. At the time the invention was made Mr Obermiller was the only inventor who was employed by Cook. The question raised in this case was whether Cook, the applicant for the PCT application, was entitled to a valid priority claim to the date of the earlier US patent application, given that the original US application was filed in the name of the inventors and not Cook itself.

At the time of the filing of the PCT application the only interest that Cook had was via Mr Obermiller’s contract of employment, and as such Mr Obermiller’s interest in the application did indeed belong to Cook. The interests of the remaining inventors, Mr Osse and Ms Thorpe were eventually assigned to Cook, 21 months after the application had been filed in Cook’s name, albeit before the grant of the patent.

Right to Priority Claim

Cook believed that it had a right to priority because it had acquired all the rights in the invention before grant of the patent. This point was disputed by Edwards Lifesciences LG (Edwards), who claimed that the right of priority may only be enjoyed by the person who filed the priority application or his successor in title at the date that the right of priority is claimed. According to Edwards priority would only have been valid if the later application had be filed in the name of the properly entitled co-owner as at the date of the later filing.

This dispute was resolved by considering the proper interpretation of Article 4 of the Paris Convention, which states 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. Thus, the benefit of claiming priority is not afforded to any person who did not file the earlier application or is not his successor in title. It was further held that the position does not change even if the title to the invention is acquired subsequent to the claim to priority because he was not entitled to benefit from the priority when the application was filed and priority was claimed.

Cook’s submission that it should be entitled to the priority claim was based on the fact that it was entitled to make the application for the patent and became successor in title to all the inventors as a result of the assignment that occurred after the filing date of the later application and because it was ultimately entitled to the grant of the patent, the same must apply in relation to priority. This contention was rejected because the entitlement to a patent is a separate issue to the entitlement of priority.

In conclusion, Cook was not entitled to make a claim to priority at the time of filing the PCT application because it was not the applicant or the successor in title for the earlier application. Moreover, the acquisition of rights subsequent to the filing of the application did not alter the position, nor was it sufficient that Cook had owned Mr Obermiller’s interest in the invention.


This case clarifies that in the event of an appropriately worded employment contract assigning intellectual property rights, it is likely that at least beneficial ownership will be transferred by virtue of employment from the employee to the employer. However, in the case of contractors and in the absence of a contract or assignment explicitly transferring the intellectual property rights from the contractors to the company, the right to claim priority belongs to the contractors.

This case stresses the importance of execution of an assignment between the inventors (especially in the case of US applications where the inventors are listed as applicants) and the company prior to filing a subsequent overseas application claiming the earlier US priority.

An invalid priority claim may have serious repercussions relating to relevant prior art and therefore the validity of a patent. Consequently, when filing patent applications and in order to avoid any ambiguity relating to the priority claim, it is imperative that the named applicant(s) on a patent application is the same person who filed the earlier application, or is already the successor in title to such a person by virtue of an appropriate assignment. On a final cautionary note, this case should not be taken to mean that all employment contracts are effective in transferring the right to claim priority to the employer; the language of the relevant clauses will be determinative in each case.