4Regulations may, in relation to Class 1 contributions, make provision—
(a)for calculating the amounts payable according to a scale prepared from time to time by the Secretary of State or otherwise adjusting them so as to avoid fractional amounts or otherwise facilitate computation;
(b)for requiring that the liability in respect of a payment made in a tax week, in so far as the liability depends on any conditions as to a person’s age or retirement, shall be determined as at the beginning of the week or as at the end of it;
(c)for securing that liability is not avoided or reduced by a person following in the payment of earnings any practice which is abnormal for the employment in respect of which the earnings are paid; and
(d)without prejudice to sub-paragraph (c) above, for enabling the Secretary of State, where he is satisfied as to the existence of any practice in respect of the payment of earnings whereby the incidence of Class 1 contributions is avoided or reduced by means of irregular or unequal payments, to give directions for securing that such contributions are payable as if that practice were not followed.