2.—(1) contribution period shall be one of not less than one year, and begins on the first day of the month following the expiry of a period of one month from the date of acceptance of the election by the Department.
(2) The contribution period and the past period shall be such that
A + Bdoes not exceed 15 per cent of the person's contributable salary for the time being,
where—
A is the rate at which the additional contributions are payable; and
B is the rate at which he pays other contributions under Part C (except any treated for the purposes of regulation G2 as employer’s contributions) or towards the provision of a pension otherwise than under these Regulations.