51.—(1) Where contributions (other than Class 1A, Class 1B or Class 4 contributions) are paid which are of the wrong class, or at the wrong rate, or of the wrong amount, the Board may treat them as paid on account of contributions properly payable under the Act.
(2) Where the whole or any part of a Class 1A contribution or a Class 1B contribution falls to be returned by the Board to any person under regulation 52(1) or any part of a Class 1A contribution falls to be repaid by the Board to any person under regulation 55(1), the Board may treat—
(a)the amount of the Class 1A contribution or, as the case may be, any part of such a contribution, as a payment on account of any secondary Class 1 contributions, Class 1B contributions or Class 2 contributions;
(b)the amount of that Class 1B contribution or, as the case may be, any part of such a contribution, as a payment on account of any secondary Class 1 contributions, Class 1A contribution or Class 2 contributions,
properly payable by that person.