2.—(1) The contribution period must 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 Secretary of State.
(2) The contribution period and the past period must be such that
A + B
does not exceed 15% 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 employers' contributions) or towards the provision of a pension otherwise than under these Regulations.