Section 71 of the Pensions Act is hereby amended by the substitution for subsection (3) of the following subsection:

"(3) Where, on commencement of this Part, any rule of a scheme is rendered null and void by subsection (1), then, during such period as may be prescribed, beginning on such commencement and not being longer than 6 years (or in the case of retirement ages, a period not being longer than 25 years) nothing in this Part shall preclude rights or obligations, relating to a period of membership in that scheme prior to the 17th day of May, 1990, from remaining subject to the provisions of the scheme in force during that period of membership.".