Where for any year there are payable by or in respect of an earner Class 4 contributions under section 15 of the Act and also primary Class 1 or Class 2 contributions or both primary Class 1 or Class 2 contributions, the liability of that earner for such Class 4 contributions for that year shall (without prejudice to his liability in the first instance for the full amount payable apart from this regulation) not exceed such amount as, when added to the amount of such other of those contributions as are ultimately payable by or in respect of him for that year, equals in value the sum of the amount which, but for the provisions of this regulation, would be payable by that earner on profits or gains equal to the higher of the two money sums specified in section 15(3) of the Act and, subject to the provisions of section 12 of the Act and regulations 63 to 65, 53 times the amount of a Class 2 contribution payable for that year.

For the purpose only of determining the extent of an earner’s liability for Class 4 contributions under paragraph (1), the amount of any primary Class 1 contributions paid at less than the primary percentage specified in section 8(2) of the Act shall be treated as equal to the amount of any primary Class 1 contributions payable at that percentage on the same amount of earnings.