Section 21 of the Principal Act is amended by the insertion of the following after subsection (1):
"(1A) Where the amount of the balance of tax remaining to be paid in accordance with section 19(3)(aa)(ii)(II) by an authorised person referred to in section 19(3)(aa)(iv)(III) (in this subsection referred to as the 'balance') represents more than 20 per cent of the tax which the authorised person became accountable for in respect of his accounting period, then, for the purposes of this subsection, that balance shall be deemed to be payable on a day (in this subsection referred to as the 'accrual day') which is 6 months prior to the final day for the furnishing of a return in accordance with section 19(3)(aa)(ii)(II) and simple interest in accordance with this section shall apply from that accrual day, however, where an authorised person can demonstrate to the satisfaction of the Collector-General that the amount of interest payable on the balance, in accordance with this subsection,