In G 3/04 (OJ 2006, 118) the Enlarged Board held that the valid intervener acquired the status of an opponent, irrespective of whether the intervention occurred during the proceedings before the opposition division or at the appeal stage. In either case his rights and obligations were the same as those of other opponents. An intervener in proceedings before the opposition division has a right of appeal under Art. 107 EPC. For the appeal to be validly filed, he must pay the appeal fee under Art. 108, second sentence, EPC. Furthermore, the board held that an intervener in proceedings before the opposition division, where all the opponents have withdrawn their oppositions, can continue the proceedings alone and, if need be, file an appeal, since he has the same status as an opponent under Art. 99 EPC 1973.

In T 614/13 of 2 July 2015 date: 2015-07-02 the board had to rule on the admissibility of an intervener's appeal against the opposition division's decision to reject its opposition because it had not shown that it had intervened in the opposition proceedings in time. The board held that, even if it upheld the opposition division's decision, that would not mean the intervener had never been a party to the proceedings, but only that as from the date on which decision on appeal took effect it would no longer be entitled to take part in the (further) proceedings. Until that point in in time its procedural status would be confined to obtaining clarification as to whether it was entitled to take part.