(1) Subject to subsection (2), this section applies to a contribution payable under any of the following provisions:

(a) section 21(1);

(b) section 26(1);

(c) section 29(1);

(d) section 30F.

(2) This section shall not apply to contributions payable on emoluments to which Chapter 4 of Part 42 of the Act of 1997 applies.

(3) Where, by virtue of any amendment to this Act, a person is required to pay a contribution to which this section applies at different rates, or in different amounts, in two parts of a contribution year, the rate of the contribution payable by the person in respect of the contribution year shall be determined by the following formula -

((A x C) + (B x D)) /12

where -

A is the first rate,