3 For the purposes of section 17(2)(a) of the Act (contribution in respect of income payable where disposable income is above a specified yearly amount but not to exceed a specified proportion of the excess):–
(a) there shall be substituted for the yearly amount of £3,060 specified in that section the yearly amount of £2,293; and
(b) there is prescribed one third as the proportion of the excess (excess of disposable income which a contribution cannot exceed).