Deduction timing: deductibility allowed only in the year the withheld tax is actually paid, tied to section 139(1) due date. Amendment links disallowance under section 40(a)(ia) to non-payment of tax on or before the due date in section 139(1) instead of the last day of the previous year, and inserts a proviso permitting deduction in the year in which such tax is actually paid where tax was deducted later or paid after the section 139(1) due date.