Over the past decade, the effective performance by the UN Security Council of its primary responsibility in the area of peace and security has increasingly become contingent on the implementation of its decisions within the national legal systems of the UN Member States. An examination of this issue in the context of the British legal system could offer a useful case-study of the ways to enhance the effectiveness of the UN collective security mechanism, to enforce the limits on the legitimacy of that mechanism, and also to highlight the practical difficulties that may accompany the attempts to apply Security Council resolutions domestically. This contribution exposes all these issues, focusing on the practice of the uk courts over the past decade. It examines the mediation of the effect of Security Council resolutions into English law through the 1946 United Nations Act, the royal prerogative and other common law techniques. After that, the contribution moves on to examine the English courts’ handling of the normative conflict between a Security Council resolution and other sources of international law.