An opposition division's refusal to consider evidence filed in due time infringes a party's fundamental right to free choice of evidence and the right to be heard (T 142/97, OJ 2000, 358). Pursuant to Art. 113(1) EPC each party must be allowed to comment on any evidence legitimately submitted in the proceedings. Allowing one party, even the party having originally submitted that evidence, unilaterally and arbitrarily to require that such evidence to be excluded from consideration would infringe this right (T 95/07).
As a rule, if assertions made in an unsworn witness declaration ("eidesstattliche Versicherung") remain contested, a request from a party to hear the witness must be granted before these assertions are made the basis of a decision against the contesting party. In T 474/04 (OJ 2006, 129), the opposition division had revoked the patent in suit because the invention did not involve an inventive step over the prior use evidenced in the declaration in lieu of an oath. Since fundamental assertions made in the declaration had been contested, the author was offered as a witness. Although the appellant (patentee) had consistently demanded that the author be heard, the opposition division decided not to summon him as a witness, even though he was available. In the board's view, the appellant had effectively been prevented from making use of a decisive piece of evidence. Thus, the opposition division had infringed the appellant’s right to be heard, which constituted a substantial procedural violation justifying the remittal of the case to the department of first instance.
While it is well-established by case-law that third party observations can be considered, both at first instance and on appeal, there is no obligation on the board beyond such consideration and no right of a third party to be heard on the admissibility of its observations and of any evidence in support of observations. While, of course, the actual parties to proceedings have the right to be heard in relation to such observations if they might (in whole or in part) form the basis of a decision, that right arises quite independently under Art. 113(1) EPC. Thus, the admissibility of third party observations (and accompanying evidence) is entirely a matter for the board (T 390/07).
In T 267/06 an affidavit with an attached, undated drawing (item D12) and a witness hearing had been offered as evidence of the public prior use claimed in the notice of opposition. The opposition division had rejected the opposition to the European patent. The only reference it had made in its decision to the offer of a witness hearing as evidence was in the "Summary of facts and submissions", while the reasons dealt exclusively with the item D12 affidavit and drawing. In the board's view, essential details referred to in the affidavit and deemed to be illustrated in the drawing seemed not to have been taken sufficiently into account by the opposition division. In those circumstances, the witness hearing offered as further evidence should not have been disregarded for the purposes of assessing the claimed public prior use as per D12. This amounted to a fundamental procedural violation as it deprived the opponent of the opportunity to exercise the right to be heard under Art. 113(1) EPC.