D10.—(1) Where (apart from this regulation) any person would be entitled to a retirement pension or to a retirement grant under two or more regulations in respect of the same period of membership—
(a)he may elect by notice in writing, given to the employing authority before the expiry of the period of three months beginning with the day on which he becomes so entitled, under which provision he is to be paid those benefits; and
(b)if he makes no such election, the employing authority may notify him in writing of the provision.
(2) Paragraph (1) is without prejudice to regulations D17, D19 and D20 and section 13(6) of the Pension Schemes Act 1993(1).