PAYE regulations may provide for a PAYE settlement agreement to allow sums which an employer is to account for—
(a)to be computed, if two or more persons hold employments to which the agreement relates, by reference to a number of those persons all taken together;
(b)to include sums representing income tax on an estimated amount taken to be the aggregate of the amounts of PAYE income consisting of—
(i)taxable benefits provided or made available by reason of the employments to which the agreement relates, and
(ii)expenses paid to the persons holding those employments; and
(c)to be computed in a manner under which they do not necessarily represent an amount of income tax which would be payable (apart from the agreement) by persons holding employments to which the agreement relates.