(f)[ any sum payable by the assessee as an employer in lieu of any leave at the credit of his employee,] [<SPAN class=amd2><A TITLE =], shall be allowed (irrespective of the previous year in which the liability to pay such sum was incurred by the assessee according to the method of accounting regularly employed by him) only in computing the income referred to in section 28 of that previous year in which such sum is actually paid by him:
