Since the introduction of EPC 2000 on 13 December 2007, it has been possible for a proprietor to limit the claims of their granted European patent, an option that was previously only available if the patent was opposed. The limitation procedure seems, at least on the face of it, quite straightforward. A request is made by the proprietor (or their representative) under Article 105a. Provided the limitation fee is paid and the request complies with the other requirements of Rules 90-96 EPC, the request will be accepted and a new published patent published as a B3 specification.
A question immediately then comes to mind: how long does it take for a request for limitation to be allowed? Patentees will not do such a thing on a whim, but will have a good reason for needing to amend their patent, probably to overcome a potential flaw due to prior art discovered after the patent was granted. Without limiting the patent, it might be more difficult and more expensive to use the patent against others. In such cases, infringement proceedings may already be in the proprietor's mind. Speed may therefore be of the essence.
To try to get an idea of what the answer might be, I looked at the EPO's publication server, and searched for all B3 specifications published from the end of 2007. There have to date been 110 such publications. Going through the Register entries for each of them, I entered the dates on which the request was made, when it was allowed and when the decision was made to limit the patent, after which the B3 specification would be published.
The results, shown in the chart below, are a little surprising. The average time taken between a request for limitation and the date on which the request is allowed is 202 days, with a standard deviation of 151 days. Taking into account the time taken between allowing the request and the date of the decision to limit the patent, the average time lengthens to 324 days, with a standard deviation of 170 days. A typical case might therefore take a year or so before a decision is made on limitation. This seems quite a long time, given that there is no substantive examination of a limitation request, only that it has to be a limitation of the scope of the patent.
The shortest time taken between request and allowance was for EP 1242105, which took only 33 days to be allowed. This was, however, a request for a very simple limitation to the claims. Perhaps this was why it didn't take very long to assess. Unfortunately, this alone does not seem to give much of a clue as to how to get a request for limitation allowed quickly. The longest time taken between request and allowance was for EP 1177920, which took a remarkable 987 days to be allowed, and 1056 days to be finally decided. This one was also fairly simple, so might just have fallen down the back of a filing cabinet for a couple of years before anything was done. Who knows.
The requests in between these extremes have all sorts of other interesting features, some of which lengthen the procedure due to the proprietor's actions, others due to the EPO being slow. The only conclusion I can reach at this point seems to be that, if you want to get your limitation allowed quickly, make it simple and straightforward to see what the limitation is (preferably by amending the B1 publication itself, so the examiner can see what you have in mind), and follow it up if nothing is heard for over a month. Other than that, it seems to be down to the usual whims of the EPO how long it will take. Don't be surprised if it takes a year or more to get it done.
The spreadsheet used to generate the chart can be accessed via Google Documents here.