The Third Schedule to the Principal Act is hereby amended by -
(a) the insertion after paragraph (4) of Rule 1 of the following proviso:
"Provided that, where such income is attributable to a period prior to the year immediately preceding the date of calculation but is received in a subsequent year, it shall be regarded for the purposes of this paragraph as having been received in the year to which it is attributable.",
(b) the insertion after paragraph (2) of Rule 2 of the following paragraph:
"(3) In the case of a person to whom paragraph (1) applies, where the income or the yearly value of the property taken to be part of his means for the purposes of that paragraph has reduced since the date of calculation, the calculation may be revised, subject to such conditions and in such circumstances as may be prescribed, but regulations made under this paragraph shall not cause the income or the yearly value of the property taken to be part of his means to be increased.",
(c) the subst