In some special cases it is possible to oppose a granted European patent even after expiry of the opposition period.
Article 105EPC provides a means for an alleged infringer to intervene in pending opposition proceedings before the European Patent Office (EPO) against a granted European patent provided the alleged infringer can prove that:
(a) Proceedings for infringement of the same European patent have been instituted against him; or (b) Following a request of the proprietor of the European Patent to cease alleged infringement, the third party has instituted proceedings for a ruling that he is not infringing the patent.
It is however important that the intervention is filed in accordance with the Implementing Regulations of the EPC. The notice of intervention shall be filed and the official fee be paid within three months of the date on which any of the above proceedings are instituted to be deemed admissible. The requirement of the form and content of the notice of intervention corresponds to those of a notice of an opposition.
European patent, opposition, Article 105EPC, EPO