"4. (1) For the purposes of this Act, there shall for every tax year be - (a) a lower earnings limit [the “LEL”] for Class 1 contributions, being the level of weekly earnings at which employed earners become liable for such contributions in respect of the earnings from their employments; ... (2) Subject to section 6 below, where in any week earnings are paid to or for the benefit of an earner in respect of any one employment of his, being employed earners employment and (a) he is over school leaving age; and (b) the amount paid is equal to or exceeds the current lower earnings limit (or the prescribed equivalent in the case of earners paid otherwise than weekly), there shall be payable, in accordance with this section (and except as provided by this Act, without regard to any other payment of earnings to or for the benefit of the earner in respect of any other employment), a primary and a secondary Class 1 contribution. (3) The primary contribution shall be payable by the earner and the secondary contribution shall be payable by the secondary Class 1 contributor."
"11. For the purpose of earnings related contributions, where an earner is concurrently employed in more than one employed earner's employment under the same employer, the earnings paid to or for the benefit of the earner in respect of those employments shall not be aggregated if such aggregation is not reasonably practicable because the earnings in the respective employments are separately calculated."
"6A. (1) Where a person is, … , or ceases to be a director of a company during any year the amount ... of earnings related contributions payable in respect of earner ... shall ... be assessed on the amount of such earnings paid (whether or not paid weekly) in the earnings periods specified in the following paragraphs of this regulation. ... (3) Where a person is a director of a company at the beginning of the year the earnings period in respect of such earnings shall be that year, whether or not he remains such a director throughout the year. (4) Where the earnings paid in respect of two or more employed earner's employments fall to be aggregated and the earnings period in respect of those earnings would be different lengths then -- (a) if those periods are determined only by the preceding paragraphs of this regulation, or (b) if the length of one or more of those periods is determined by the preceding paragraphs of this regulation and the length of one or more of the others is determined by any other provision of these regulations, the earnings period in respect of all those earnings shall be the period determined by those paragraphs or, where there is more than one such period for longer, or as the case may be, longest period so determined."