Defence and security policy lies at the heart of the British state, but can appear entirely untrammelled by the constitution. In fact, when political and military leaders exercise their executive powers, Parliament and the judiciary have limited oversight, let alone control, over their actions. Defence and the UK Constitution introduces key constitutional issues to a general audience and pinpoints the differences between the ‘legal constitution’ and the ‘political constitution’, with reference to the lack of accountability within modern British security structures. Professor Nigel White traces this imbalance back to the 1680 Bill of Rights and examines the evolution of war and emergency powers, placing them within the context of international law. Advocating for a rebalancing of the efficient and democratic, as well as the legal and political, elements of the constitution, this short work aims to address the inherent ‘defence paradox’ in the UK constitution and to indicate which constitutional changes are needed to safeguard our democratic principles and limit excessive uses of discretionary power.