Proceedings before the EPO provided for in respect of European patent applications and patents are governed by the principle of party disposition (ne ultra petita), according to which the procedure is with some exceptions initiated on request, and the principle of ex officio examination laid down in Art. 114(1) EPC, according to which the EPO examines the facts of its own motion and is not restricted by the arguments or requests of the parties (see G 9/92, OJ 1994, 875; G 4/93, OJ 1994, 875). Certain restrictions have, however, been placed upon the principle of ex officio examination in order to make EPO proceedings clearer, accelerate them and therefore limit the risks to the parties. The principle is likewise subject to restrictions with respect to the examination of the grounds for opposition, but this is less a question of competence than of a consistent application of procedural principles.
Opposition proceedings are pending only in so far as the patent is contested in the "statement of the extent to which the European patent is opposed" prescribed under R. 76(2)(c) EPC (former R. 55(c) EPC 1973). Subject-matter not challenged in the statement is therefore not the subject of "opposition" within the meaning of Art. 101 EPC or "proceedings" within the meaning of Art. 114 and 115 EPC. Accordingly, the opposition division or board of appeal could only rule on the revocation or maintenance of a patent to the extent that it was contested in the notice of opposition. Exceptionally, however, the opposition division could consider other grounds for opposition, which, prima facie, in whole or in part would seem to prejudice the maintenance of the European patent (G 9/91, OJ 1993, 408; see also G 10/91). To reflect this case law, the wording of Art. 101(1) EPC was changed in the revised text to make it clear that the opposition division is not necessarily obliged to examine all the grounds for opposition ("at least one ground for opposition").
Following the decision in G 10/91, the board held in T 274/95 (OJ 1997, 99) that, if a ground for opposition was substantiated in the notice of opposition but was subsequently not maintained during the opposition division proceedings (in the case in question, a statement to that effect had been made by the opponent during oral proceedings), the opposition division was under no obligation to consider this ground further or to deal with it in its decision, unless the ground was sufficiently relevant to be likely to prejudice maintenance of the patent.
In T 223/95 the appellant had argued that the opposition division should take steps of its own motion to establish by investigation the level of knowledge of the person skilled in the art. The board observed that such an investigative approach would not be consistent with the character of the postgrant opposition proceedings under the EPC, which were in principle to be considered as contentious proceedings between parties normally representing opposite interests, who should be given equally fair treatment. In the board's opinion, it was unrealistic to suppose that the opposition division could seek, gather and select evidence in an entirely impartial fashion; herein lay an essential distinction between the functions of the examining divisions and the opposition divisions. For that reason it was the responsibility of the opponent himself to present to the opposition division the facts, evidence and arguments in support of the grounds on which the opposition was based.
As regards the investigative power of the boards under Art. 114(1) EPC, read in conjunction with in R. 100(1) EPC (R. 66(1) EPC 1973), it is their judicial character that sets the limits to this power. To permit the shifting of the legal and factual framework of the opposition in appeal, in a mistaken reliance on the wording of Art. 114(1) EPC, read in isolation from the rest of the EPC, and in particular R. 100(1) EPC, would offend the legal principles contained and expressed in the EPC and explained in the case law of the Enlarged Board (see e.g. T 737/92).