5.—(1) Scheme regulations may provide that where a pension in payment under a scheme to which section 18(1) or 32(2) applies has been calculated by reference to this Schedule, the pension cannot be recalculated by reference to this Schedule where there is a subsequent period of pensionable public service (within the meaning of paragraph 3).
(2) Provision made under sub-paragraph (1) may in particular be made by amending the scheme under which the pension is in payment.