Excise duty exemption for plated iron wire prevents recovery of excess duty where prior practice omitted levy. The Government declares an excise duty exemption for wire of iron or non-alloy steel plated or coated with base metals within the relevant tariff heading, finding that a practice prevailed of not levying duty above a specified threshold per tonne for clearances between 14-5-1992 and 25-6-1992; it directs that duty in excess of that threshold need not be paid where such excess was not levied during that period in accordance with the practice.