(1) The funds required—
(a) for paying such benefits under Part II below as are payable out of the National Insurance Fund and not out of other public money;
(b) for the making of payments under section 134 below towards the cost of the national health service and into the Redundancy Fund ; and
(c) for paying benefit under the Old Cases Act,
shall be provided by means of contributions payable to the Secretary of State by earners, employers and others, together with the Treasury supplements specified in subsection (5) below.
(2) Contributions under this Part of this Act shall be of the following four classes—
Class 1, earnings-related, payable under section 4, being—
primary Class 1 contributions from employed earners, and
secondary Class 1 contributions from employers and other persons paying earnings ;
Class 2, flat-rate, payable weekly under section 7 by self-employed earners;
Class 3, payable under section 8 by earners and others voluntarily with a view to providing entitlement to benefit, or making up entitlement; and
Class 4, payable under section 9 in respect of the profits or gains of a trade, profession or vocation, or under section 10 in respect of equivalent earnings.
(3) The amounts and rates of contributions in this Part and the other figures therein which affect the liability of contributors shall—
(a) be subject to regulations under sections 128 to 132 below (H.M. forces, mariners, married women, widows and others); and
(b) to the extent provided for by sections 120 and 122 (re-rating), be subject to alteration by orders made by the Secretary of State from year to year under those sections.
(4) Schedule 1 to this Act—
(a) shall have effect with respect to the computation, collection and recovery of contributions of Classes 1, 2 and 3, and otherwise with respect to contributions of those classes; and
(b) shall also, to the extent provided by regulations made under section 10, have effect with respect to the computation, collection and recovery of Class 4 contributions, and otherwise with respect to such contributions, where under that section provision is made for contributions of that class to be recovered by the Secretary of State and not by the Inland Revenue under section 9(1) to (4).
(5) Subject to section 129 below (mariners, airmen etc.), there shall by way of supplement to contributions be paid out of money provided by Parliament, in such manner and at such times as the Treasury may determine, amounts the total of which for any year is equal to 18 per cent. of so much of all contributions (of the four classes) paid in that year as remains after deducting the appropriate national health service allocation and the appropriate allocation to the Redundancy Fund.
(6) No person shall—
(a) be liable to pay Class 1 or Class 2 contributions unless he fulfils prescribed conditions as to residence or presence in Great Britain;
(b) be entitled to pay Class 3 contributions unless he fulfils such conditions; or
(c) be entitled to pay Class 1 or Class 2 contributions other than those which he is liable to pay, except so far as he is permitted by regulations to pay them.