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Admissibility of documents submitted by interveners at EPO appeals

Any third party may intervene in ongoing opposition proceedings for a European patent after the deadline for filing an opposition has expired if infringement proceedings relating to that patent have been instituted against them or if they have instituted proceedings for a non-infringement ruling following a request from the patent proprietor to cease an allegedly infringing action in relation to a patent.

Since opposition proceedings are deemed to be ongoing whilst the outcome of the opposition is being appealed (or may still be appealed), this also allows third parties to intervene until the appeal has been decided (or, if no appeals are filed, until expiry of the period for filing an appeal).

In the recent decision, T1665/16, the Boards of Appeal discussed the ability of a third party to intervene at the appeal stage and, in doing so, introduce new prior art documents into the proceedings that would be inadmissible if they had been filed by an opponent already party to the proceedings.

In this specific case, two interventions were filed, raising a lack of novelty over 20 new documents. However, both interveners later withdrew their interventions before the hearing. At the hearing, the appellant (i.e. the original opponent) argued that they were entitled to rely on the 20 new documents filed by the interveners despite the withdrawal of the interventions because the documents had nevertheless been validly introduced into proceedings, whereas the patentee argued that the documents had not been filed as part of the initial appeal and were therefore filed late and should be dismissed.

The Board of Appeal found that the documents had not been filed late since time periods set for filing an opposition or an appeal have no bearing on when an intervention may be filed. The Board therefore allowed the documents into the proceedings and found that the appellant was entitled to rely on them. However, since the new documents related to parts of Claim 1 that had not been considered by the parties prior to the interventions, the Board remitted the case back to the Opposition division for reconsideration.

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