In G 3/99 (OJ 2002, 347), the Enlarged Board also held that, in an opposition filed in common, there had to be in all cases a common representative (Art. 133(4) EPC 1973 and R. 100 EPC 1973). Only that common representative is entitled to act in the opposition proceedings on behalf of all the common opponents taken as a whole and to sign the filed documents. Since the EPO treats a procedural act performed by a non-entitled person in the same way as a missing signature (see T 665/89), each common opponent or any other person acting on his behalf could perform such an act to avoid missing a deadline, provided the deficiency is remedied within an additional period set by the board in the communication under R. 36(3) EPC 1973 (R. 50(3) EPC), notified to the common representative and sent for information to the non-entitled person who performed the act. The deficiency is remedied once the procedural act is signed by the common representative.

According to the Enlarged Board, in order to safeguard the rights of the patent proprietor and in the interests of procedural efficiency, it had to be clear throughout the proceedings who belonged to the group of common opponents or common appellants. If either a common opponent or appellant (including the common representative) intended to withdraw from the proceedings, the EPO had to be notified accordingly by the common representative or by a new common representative determined under R. 100(1) EPC 1973 in order for the withdrawal to take effect.

Referring to this case law in its interlocutory decision in T 482/02 of 9 February 2005 date: 2005-02-09, the board stated that, where it was doubtful whether an opposition had been filed on behalf of a body which enjoyed legal personality in its own right or on behalf of several natural persons acting in common, the opponents (here a UK partnership) should be invited to establish that the body was a legal person or an equivalent thereto. If this was not established, the opposition was to be considered as having been filed on behalf of the several natural persons as common opponents (see also T 866/01). In that case the opponents still had to furnish the names and addresses of the partners in order to comply with R. 55(a) EPC 1973 (R. 76(2)(a) EPC). If this information was not received within a period specified by the board, the opposition had to be rejected as inadmissible under R. 56(2) EPC 1973 (R. 77(2) EPC), irrespective of whether or not such information would have been sufficient to prevent rejection under R. 56(1) EPC 1973 (R. 77(1) EPC).

Similarly, in T 315/03 (OJ 2005, 246), the board followed G 3/99, adding that, while the admissibility of an opposition by multiple opponents had to be kept under review throughout the proceedings, parties could not expect the opposition division or board to do this alone. It was clear that the board had neither the resources nor the knowledge of the relevant laws of all the contracting states necessary to police the composition of, and the legal status of all members of, multiple opponents. Once prima facie admissibility was acknowledged, it had to be up to the party or parties seeking to challenge admissibility to make a case of inadmissibility.

With regard to changes over time in the composition of a multiple opponent, the board agreed with the respondent that the absence over eleven and a half years of any notification concerning the 1200 members of opponent 6 ("opposition club") could in itself be considered an indication that the "clear throughout" condition had not been complied with. On the other hand, the fact that certain opponents only came into being for the purpose of filing opposition to one patent could not in itself be an objection to admissibility; an opponent's motive or lack of motive was irrelevant (see G 3/97, OJ 1999, 245). Similarly, it appeared to the board to be wholly irrelevant that an opponent, whether individual or multiple, might be supported by others (e.g. employees or shareholders of a company which was a party). Such supporters clearly could not take any part in the proceedings and could not affect its outcome. Moreover, the support for a party could not per se be a reason to challenge admissibility.