Paragraph (f) of Case 14 in Schedule 3 to the [1968 c. 23.] Rent Act 1968 and paragraph (f) of Case 15 in Schedule 3 to the [1971 c. 28.] Rent (Scotland) Act 1971 (under which the right conferred by those Cases to recover possession of a dwelling-house is available only if proceedings are commenced within the appropriate time limit specified in those paragraphs) shall cease to have effect except where the relevant date for the purposes of the said Case 14 or, as the case may be, Case 15 was before the passing of this Act.