How to lose priority in 3 ways

How to lose priority in 3 ways

“Priority”. A word that can strike fear into even the most seasoned of IP attorneys. While on the face of it, the law concerning priority at the EPO can seem fairly straightforward, there are a few things that can trip you up if you’re not prepared (and some that are not fixable, no matter what you do).
Here is our guide to common priority pitfalls, and a few tips on how you might be able to deal with them.

Why bother with a priority application?

Priority applications are generally used to “cut off” the date at which prior art can be cited against the claimed invention up to 12 months before the filing date of a PCT or national application. It is often the case that the inventors or Applicant publishes information about the invention in the priority year which, if it became available as prior art, would kill the case in question. Therefore, it may be critical the case is validly entitled to priority.

Who looks at priority?

Priority entitlement is not typically looked at in detail, if at all, during prosecution at the EPO. However, if it subsequently determined (e.g. during opposition or appeal proceedings) the claim to priority is not valid, there is often little that the Applicant/Patentee can do to fix it.
In order to avoid this situation, there are a few things attorneys should consider when filing later applications claiming priority from an earlier application.

What is needed to validly claim priority?

While we all know the later application must be filed within 12 months of the earlier (priority) application, there are three more things that should be borne in mind. These are:

  1. The priority application must relate to the same invention as claimed in the later application

  2. The priority application must be the first application to disclose the subject matter of the claimed invention

  3. The later application must be filed by the same person as the priority application, or their successor in title

We address each of these below in more detail. 

1. The same invention

Sometimes a priority application might not have the exact same disclosure as that of the later application. For example, new information might be added during the priority year as developments are made to the invention.
Any “new” subject matter added at this time runs the risk of not being entitled to priority. Whether or not the priority application is determined to relate to the “same invention” as claimed in the later application will vary between patent offices. However, at the EPO, it is very strictly assessed, and in fact the same test as “added matter” is applied to make this assessment. In other words, the EPO look to see if the priority document “directly and unambiguously” discloses the claimed invention. If not, the claims are not entitled to priority.

2. The first application

If the priority application is not the first application by the Applicant (or their successor in title) to disclose subject matter falling within the scope of the claimed invention, then your priority claim may be invalid.
This requirement can be particularly tricky when it comes to Continuation in Part applications (CIPs).
For example, if there is another application by the same Applicant (which can be a priority document for another case) filed more than 12 months before your later application, which also discloses subject matter overlapping within the claims of your later application, then your priority application may not be the “first application” to disclose that subject matter. As such, you may not be able to validly claim priority for that subject matter.
It is sometimes possible to fix this issue by excluding / deleting the overlapping subject matter. However, this can be tricky in view of “added matter” requirements at the EPO.

3. The same person (or successor in title)

The EPO requires that the "same" person, or their successor in title file both the priority application and the subsequent application. This is an issue that cannot be corrected retroactively, and so may be terminal to the priority claim of the application in question, and all cases stemming from that application (i.e. all divisional applications).
If the priority document was not filed by the "same" person as the later application, then it is necessary to show that the rights in the invention passed from each person named on the priority application to whoever is named on the later application. This transfer must have occurred before the filing date of the later application.
This issue can be particularly tricky for cases where the priority application is filed in the name of the inventors, but the later application is filed in the name of the applicant. If there is no written proof predating the filing date of the later application that the transfer occurred for each inventor, then it is often difficult to show the person named on the later application was entitled to claim priority from the priority application.
If sufficient proof cannot be provided, the priority claim may be deemed invalid.
The EPO recently addressed this issue in the famous CRISPR appeal (T844/18), in which the Board of Appeal considering the case confirmed there would be no change to the established approach (set out above), and in that case the loss of priority resulted in revocation of the patent in view of intervening prior art. If you would like to read more about this issue, my colleague Jamie Atkins has provided an in depth analysis of this case in recent articles (see here and here) .


To validly claim priority, you must fulfil each of the above requirements. Failing to comply with any one of them results in a loss of priority.
Given the EPO typically do not look at priority entitlement during examination, an attack on the validity of a priority claim (using all three grounds above) can be particularly powerful during EPO opposition and appeal proceedings if there is intervening prior art. This attack may be useful in offensive oppositions, given issues with priority are usually difficult to fix after the fact.

Staying in touch

If you would like further information on any of the above points, or to talk through how they might be relevant to your cases, please do not hesitate to contact Kathryn Eldridge, or your usual contact at Kilburn & Strode LLP.

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