(i) Rule 82(1) EPC
Under R. 82(1) EPC (previously R. 58(4) EPC 1973), before the opposition division decides to maintain the patent as amended, it shall inform the parties of the text in which it intends to maintain the patent and shall invite them to file their observations within two months if they disapprove of that text.
The Enlarged Board found in G 1/88 (OJ 1989, 189) that the fact that an opponent had failed, within the time allowed, to make any observations on the text despite an invitation to do so under R. 58(4) EPC 1973 did not render his appeal inadmissible.
To regard silence as betokening consent would be tantamount to withdrawal of the opposition with consequent surrender of the right to appeal. Surrender of a right could not be simply presumed. Deeming silence to be equivalent to surrender would also be inconsistent with the logic of how the EPC operated, since it would be at odds with the way in which it dealt with the loss of rights. Where the legal consequence of an omission was to be a loss of rights, this was expressly stated. Furthermore, under Art. 164(2) EPC 1973 the Implementing Regulations had always to be interpreted in the light of the EPC.
The interpretation of the Implementing Regulations which corresponded most closely to the principles of the EPC thus prevailed. It was a principle of the EPC, however, that parties' rights were safeguarded by the possibility of appeal to at least one higher-ranking tribunal. The Implementing Regulations should therefore be construed in such a way that R. 58(4) EPC 1973 was not allowed to interfere with the right of appeal under Art. 106 and 107 EPC 1973. The interpretation in the light of the sense and purpose of the procedure under R. 58(4) EPC 1973, lead to the same goal.
In T 156/90 the opponent had stated that he would have no objection to maintenance of the patent if the claims were amended in a specified way, which they were. His subsequent appeal was dismissed as inadmissible; his argument that the circumstances had changed and he was no longer bound by his consent failed.
In T 266/92, on the other hand, the opponent had declared in opposition proceedings that he would withdraw his request for oral proceedings if the patentee agreed to an amended wording of the patent, as he did. The board held that the appellant was adversely affected within the meaning of Art. 107 EPC 1973, and was entitled to appeal; withdrawal of a request for oral proceedings did not in itself imply withdrawal of any other existing request. There might be reasons other than consent - such as a wish to save costs or obtain a quicker decision - for a party who originally asked for oral proceedings to drop his request.
In T 833/90 the board held that an appeal should be considered admissible if it was not clear or ascertainable whether the opponent (appellant) had agreed to maintenance of the patent. This was followed in T 616/08.
(ii) Opponent adversely affected
In T 273/90 the board concluded that legal uncertainty arising from inadequate adjustment of the description to amended claims constituted sufficient grievance under Art. 107 EPC 1973, as the commercial interests of the appellant (opponent) could be adversely affected (likewise T 996/92).
In T 1178/04 (OJ 2008, 80) the board found the appeal filed by the opponent admissible even where the validity of the opponent's status was challenged following a disputed transfer, as a person was a party to proceedings for the purposes of Art. 107 EPC 1973 even if his entitlement to take part in such proceedings was brought into question. A decision that he was not entitled to take part in the proceedings would have the effect that he was no longer entitled to take part in the proceedings, but not that he had never been a party. See also T 1982/09.
It is not necessary for an opponent to have a continuing interest, financial or otherwise, in the prosecution of the opposition or appeal; it suffices that the decision does not accede to one of its substantive requests (T 1421/05 following T 234/86; OJ 1989, 79).
(iii) Opponent not adversely affected
In T 299/89 the board considered the extent of entitlement to appeal of an opponent who in his opposition had requested only partial revocation but in his appeal wanted the whole patent revoked. It decided that this was determined by the scope of the original request made in the opposition. The opponent was only adversely affected within the meaning of Art. 107 EPC 1973 to the extent that this request was not granted, and he could not on appeal file a wider request.
An opponent is not adversely affected by obiter dicta reasons given in a revocation decision and favourable to the patent proprietor, and which it is appropriate for the opposition division to include to obviate remittal in the event of revocation being reversed on appeal (T 473/98, OJ 2001, 231).
A respondent (opponent) which is not adversely affected by a decision revoking the patent is not entitled to file an appeal for the sake of acquiring an independent appellant status instead of the status of a respondent (party as of right) (T 193/07). The board considered that its conclusion was in accordance with the established jurisprudence of the boards of appeal (see e.g. T 854/02, T 981/01, T 1147/01, T 1341/04 and T 473/98). The board also pointed out that purely hypothetical considerations put forward by the opponent in support of the admissibility of its appeal concerning potentially disadvantageous situations that might occur (in the future) in related national litigation proceedings had no legal relevance under Art. 107 EPC.
In T 1569/11 the opponents did not seek to challenge the decision of the opposition division (i.e. revocation of the patent) but the reasons for the decision. In particular, the opponents wanted the patent to be found invalid under Art. 100(c) EPC. The board noted that, in doing so, they misunderstood the nature and purpose of opposition appeal proceedings, which are not to re-examine a patent but to decide whether or not a first instance decision is correct (cf. T 854/02; T 437/98, OJ 2001, 231; T 193/07).