21.—(1) A person entitled to retirement compensation under regulation 18 or 19 shall pay an amount equal to any sum which was paid to him by way of return of superannuation contributions (including any interest) after ceasing to be employed—
(a)if the provisions of his last relevant pension scheme enable him to be credited with benefits attributable to that sum, to the fund authority, and
(b)in any other case, to the Secretary of State.
(2) If the person does not pay as specified in paragraph (1), his retirement compensation shall be reduced by an annual amount the capital value of which is equal to the amount of the said superannuation contributions.
(3) For the purposes of this regulation the expression “superannuation contributions”