The global war on terrorism gives rise to a range of legal, political and ethical problems. One major concern for UK policy-makers is the extent to which the government may be held responsible for the illegal and/or unethical behaviour of allies in intelligence gathering—the subject of the forthcoming Gibson inquiry. The UK government has been criticized by NGOs, parliamentary committees and the media for cooperating with states that are alleged to use cruel, inhuman and degrading treatment (CIDT) or torture to gain information about possible terrorist threats. Many commentators argue that the UK's intelligence sharing arrangements leave it open to charges of complicity with such behaviour. Some even suggest the UK should refuse to share intelligence with countries that torture. This article refutes this latter view by exploring the legal understanding of complicity in the common law system and comparing its more limited view of responsibility—especially the ‘merchant's defence’—with the wider definition implied in political commentary. The legal view, it is argued, offers a more practical guide for policy-makers seeking to discourage torture while still protecting their citizens from terrorist threats. It also provides a fuller framework for assessing the complicity of policy-makers and officials. Legal commentary considers complicity in relation to five key points: identifying blame; weighing the contribution made; evaluating the level of intent; establishing knowledge; or, where the latter is uncertain, positing recklessness. Using this schema, the article indicates ways in which the UK has arguably been complicit in torture, or at least CIDT, based on the information publicly available. However, it concludes that the UK was justified in maintaining intelligence cooperation with transgressing states due to the overriding public interest in preventing terrorist attacks.