3. Where an item to which regulation 2 applies is being or has been imported, a person commissioned by the Commissioners of Customs and Excise or a person authorised by them may require any person possessing or having control of the item to furnish proof that its importation is or was not unlawful by virtue of that regulation; and if such proof is not furnished to the satisfaction of the said Commissioners the item shall be liable to forfeiture under the Customs and Excise Management Act 1979(1).