may, subject to the approval of the Commissioner, at any time within a period of two years from the date on which that duty was paid, such provisional refund was granted or such licensee became entitled to such refund, set off such duty, provisional refund or amount refundable against that particular duty for which such licensee subsequently becomes liable, except that the duty refundable in terms of the said item 534.00 be set off against the excise duty specified in Section B of Part 2 of Schedule No. 1 for which such licensee subsequently becomes liable, provided the monthly or quarterly accounts or bills of entry submitted by such licensee in respect of the payment of any duty against which any duty, provisional refund or amount refundable has been set off are accompanied by a full statement by such licensee, supported by a certificate by an officer, giving full particulars and a full account of the circumstances in respect of such set-off and by such documentary evidence as the Commissioner may in each case require.