Where a dealer makes sales of furnace oil or lubricants to any foreign going vessels in West Bengal, on or after 1st day of Novembr, 2006, such dealer may, for the purpose of determination of his turnover of sales on which tax is payable, deduct under clause (c) of sub-section (1) of section 16, from his turnover of sales seventy per centum of that part of turnover of sales which represents sale of such goods to such vessels and he shall, on demand by appropriate authority under the Act, furnish the relevant tax invoice or invoice or cash memo or bill and other related documents evidencing such sales:

Provided that no such deduction shall be allowed unless the dealer selling the goods, on demand by the appropriate authority under the Act, furnishes the relevant tax invoice or invoive or cash memo or bill and other related documents evidencing such sales.