12. The Organisation shall have relief, under arrangements made either by the Secretary of State or by the Commissioners of Customs and Excise, by way of refund of customs duty paid on any hydrocarbon oils (within the meaning of the Customs and Excise Act 1952) which are bought in the United Kingdom and necessary for the exercise of the official activities of the Organisation, such relief to be subject to compliance with such conditions as may be imposed in accordance with the arrangements.