(a) Subject to paragraph (c), a contribution (in this Act referred to as a "voluntary contribution"), in the case of a person who becomes a voluntary contributor by virtue of paragraph (a) of section 21(1) and who is under pensionable age, shall be payable in each contribution year at such time or times and in such manner as the Minister shall prescribe -
(i) at a percentage rate (as set out in paragraph (b)) of the amount of the reckonable income of the contributor in the preceding contribution year, or
(ii) where there was no such income or such income did not exceed such amount as may be prescribed, at a percentage rate of such amount as the Minister shall prescribe.
(b) A percentage rate for the purpose of paragraph (a)(i) shall be -
(i) in the case of a voluntary contributor who, immediately before ceasing to be an employed contributor, was employed in employment in respect of which the employment contributions payable are not reckonable for the purposes of old age (contr