In T 143/91 the board held that a member of an opposition division was biased if he had a personal interest within the meaning of Art. 24(1) EPC 1973. The mere fact that the member had previously been employed by a company dependent on a party to the opposition proceedings was, however, not sufficient proof of such an interest.
Under Art. 17(3) and (4) of the Service Regulations for permanent and other employees of the EPO (August 2018 version) any permanent employee who, in the performance of his duties, is called upon to decide on a matter in which he has a personal interest such as to impair his independence shall inform the President of the Office, or the President of the Boards of Appeal in the case of members of the boards of appeal.