Apportionment of single payment of earnings in respect of different employed earner’s employments by different secondary contributors
17. Where any single payment of earnings is made in respect of two or more employed earner’s employments under different secondary contributions, liability for earnings-related contributions shall be determined by apportioning the payment as follows—
(a)where the secondary contributors are, in respect of those employments, carrying on business in association with each other, to the secondary contributor who makes the payment;
(b)where the secondary contributors are not so carrying on business in association with each other, to each of those secondary contributors in the proportion which the earnings due in respect of that secondary contributor’s employment bears to the total of the single payment.