108.—(1) Where for any year there are payable (or, but for this regulation, there would be payable) by or in respect of an earner a special Class 4 contribution and also any contribution under section 15 of the Act (in this regulation referred to as “an ordinary Class 4 contribution”) or any primary Class 1 contribution or any Class 2 contribution, or any combination of such contributions, the maximum amount of the special Class 4 contribution payable for that year shall not exceed the maximum specified in paragraph (2).
(2) The maximum is—
(a)in the case of a special Class 4 contribution and an ordinary Class 4 contribution, the amount (if any) equal to the difference between the maximum amount of a special Class 4 contribution for which provision is made in section 18(1) of the Act and the amount of the ordinary Class 4 contributions ultimately payable for that year; or
(b)in any other case (whether or not a Class 4 contribution is also payable), the amount (if any) equal to the difference between the maximum amount prescribed in regulation 100 and the amount of such Class 4, primary Class 1 and Class 2 contributions as are ultimately payable for that year.
(3) Paragraphs (1) and (2) are without prejudice to the earner’s liability in the first instance for the full amount payable apart from those paragraphs.