In G 1/91 (OJ 1992, 253) the Enlarged Board held that unity of invention did not come under the requirements which a European patent and the invention to which it related had to meet under Art. 102(3) EPC 1973 (Art. 101(3)(a) EPC) when the patent was maintained in amended form. It was consequently irrelevant in opposition proceedings that the European patent as granted or amended did not meet the requirement of unity. It was clear from the "travaux préparatoires" not only that lack of unity was deliberately excluded as a ground for opposition, but also that any lack of unity arising during opposition proceedings as a result of amendment of the patent had to be accepted.

The Enlarged Board noted inter alia that although unity of invention under Art. 82 EPC 1973 was a material requirement, it was still merely an administrative regulation. It served a number of administrative purposes, particularly in demarcating the respective responsibilities of the departments. The administrative purposes of unity were fulfilled in the main up to the time the patent was granted. The purpose and intention of opposition proceedings was to give a competitor the opportunity of opposing unjustified protective rights. Since this served the competitor's interests, he did not also need to be given the opportunity of contesting a patent on the ground of lack of unity. Lack of unity did not in fact rule out patent protection; it could only result in an application being divided to produce two or more patents. See also T 830/11.