Under Art. 114 EPC the EPO has a limited obligation to undertake an examination of its own motion with regard to public prior use.
In T 129/88 (OJ 1993, 598) the board noted that although a board of appeal had an obligation under Art. 114(1) EPC to investigate matters of its own motion, that obligation did not extend as far as investigating an allegation of public prior use, where the party previously making that allegation had withdrawn from proceedings and it was difficult to establish all the relevant facts without that party's co-operation. The reason for this was that the obligation to investigate of its own motion imposed on the EPO by Art. 114(1) EPC was not unlimited in its scope, but was confined by considerations of reasonableness and expediency. Therefore, if the opponents withdrew the opposition, thereby indicating that they were no longer interested in the outcome of the opposition, then, although the EPO might have the power, depending on the state of residence of relevant witnesses, to compel them to give evidence, either before the EPO or before the court of a contracting state, in the interests of procedural economy it should not normally investigate the issue any further. It would be different if a relevant public prior use had already been substantiated by documents of undisputed authenticity, or if the material facts with respect to the alleged public prior use were undisputed (see T 830/90, OJ 1994, 713; T 887/90, T 634/91, T 252/93 and T 34/94).