(b) the securities of, or guaranteed as to principal and interest by, the Government of the United Kingdom shall be regarded as approved securities other than Government securities for a period of four years from the 1[ commencement of the Insurance (Amendment) Act, 1950 (47 of 1950 ), in the manner and to the extent hereinafter specified, namely:--
(i) during the first year, to the extent of twenty- five per cent. in value of the sum referred to in sub- section (1);
(ii) during the second year, to the extent of eighteen and three- fourths per cent. in value of the said sum;
(iii) during the third year, to the extent of twelve and a half per cent. in value of the said sum; and
(iv) during the fourth year, to the extent of six and a quarter per cent. in value of the said sum: Provided that, if the Central Government so directs in any case, the securities specified in clause (b) shall be regarded
as approved securities other than Government securities for a longer period than four years, but not exceeding six years in all, and the manner in which and the extent to which the securities shall be so regarded shall be as specified in the direction.