(1) Where any amount in respect of an employment contribution, including an amount estimated under the provisions of article 11 or 12, which -

(a) an employer is liable to pay to the Collector-General or to the Minister, as the case may be, or

(b) an employed contributor to whom paragraph (a) or (b) of section 13(4A) applies is liable to pay to the Collector-General or to the Minister, as the case may be,

is not so paid on or before the payment date, simple interest on that amount shall be paid by the employer or the employed contributor, as the case may be, and such interest shall be calculated at the rate at which, for the time being, interest is chargeable on unpaid income tax under section 991 of the Act of 1997.

(2) Interest charged on employment contributions shall be collected and be recoverable by the Collector-General or, by the Minister in the case of an employment contribution payable in respect of a special contributor, and shall be accounted for by the Collector-General or the Minister, as the case may be, and paid into the Social Insurance Fund.