12. The United Nations shall have relief, under arrangements made by the Commissioners of Customs and Excise, by way of refund of customs duty paid on any hydrocarbon oil (within the meaning of the Hydrocarbon Oil (Customs & Excise) Act 1971) which is bought in the United Kingdom and used for the official purposes of the United Nations, such relief to be subject to compliance with such conditions as may be imposed in accordance with the arrangements.