64.—(1) This regulation applies if any of the following retirement pensions becomes payable to M before the end of the contributions payment period—
(a)a partial retirement (if M has elected to receive additional pension with it);
(b)a premature retirement pension;
(c)an early retirement pension.
(2) If this regulation applies—
(a)periodic payments for additional pension cease to be payable on the entitlement day for that pension; and
(b)the amount of accrued additional pension as at the day M leaves the pensionable service concerned is an amount determined by the scheme manager, having regard to—
(i)the period over which the contributions were paid; and
(ii)the length of the contribution payment period.