(1) A contributor who is contributing for the number of units of pension ascertained in accordance with subsection (2) of section 20 having regard to his salary may, from time to time, elect to contribute for one or more reserve units of pension in accordance with this Division.
(2) Subject to subsection (4) of section 32, the number of reserve units of pension for which a contributor may contribute, together with the number of any reserve units in respect of which he has made an election under section 31 or section 32, shall not exceed twelve.
(3) Contributions for a reserve unit of pension:
(a) shall be in accordance with the Third or Fourth Schedule, whichever is appropriate, reduced by amounts, if any, ascertained in accordance with the tables of reductions of contributions set out in the Sixth Schedule; and
(b) shall be payable as from the date on which the contributor elects to contribute for that reserve unit of pension.
(4) A person is not entitled to make an election under this section after 30 June 1976, and a person shall not make contributions to the Fund for a reserve unit of pension on or after 1 July 1976 except contributions the obligation for the payment of which came into existence before 1 July 1976.