(2)     Where any antedated salary or pension has been received by or has accrued to any person during any year or period of assessment and the period in respect of which such antedated salary or pension has become payable (hereinafter referred to as the accrual period) commenced before the commencement of the said year or period of assessment, such antedated salary or pension shall at the option of the taxpayer be deemed-

(a)     if the accrual period commenced not more than two years before the commencement of the said year or period of assessment, to have been received by or to have accrued to the said person in part during each of the years or periods of assessment in which any portion of the accrual period falls (the part of the said amount relating to any such year or period of assessment being determined on the basis of a reasonable apportionment of the whole of the said amount between all the said years or periods of assessment); or

(b)     if the accrual period commenced more than two years before the commencement of the first–mentioned year or period of assessment, to have been received by or to have accrued to the said person in three equal annual instalments (the first and second instalments two years and one year respectively before the date on which the said amount accrued to the said person and the third instalment on the said date).

(3)     Where any member of the citizen force or of the commandos has bound himself to serve in such force or the commandos for a continuous period of service of at least eighteen months as contemplated in section 22 (6A) or 44 (5A) of the Defence Act, 1957 (Act No. 44 of 1957), the provisions of subsection (2) shall mutatis mutandis apply in respect of any gratuity which has become payable to him by the State upon and by reason of the completion of such period of service, as though such gratuity were antedated salary or pension granted permanently and with retrospective effect, in respect of the said period of service.