A comprehensive, detailed and updated account of UK national security law in all its aspects, National Security Law, Procedure and Practice is the only book to collate and explain all the elements of law, both substantive and procedural, and the practical issues which may arise in national security litigation. The specialised nature of the subject makes this book a vital text, not only for those seeking an overview of national security law, but also for experienced practitioners instructed to act in proceedings in which national security issues may arise. The intense media and public scrutiny which accompanies many national security cases makes this book of interest to a wider audience seeking to understand the legal context of such cases. This new edition draws on the professional experience of a team of expert contributors and covers all recent legislation, case law and guidance. It provides a detailed explanation of the National Security Act 2023, which repeals and replaces the existing law relating to state threats. The new Act introduces significant new offences and executive powers, including the power to impose state threat prevention and investigation measures ('STPIMs'), and creates a new scheme for the registration of foreign political influence activities. The second edition also includes analysis of the landmark Supreme Court decision in Shamima Begum, which re-evaluates the respective roles of the government and the courts in national security matters and has ramifications throughout the work; a comprehensive explanation of the National Security and Investment Act 2021; a fully revised chapter on sanctions law; and an updated explanation of the continued impact of EU law on UK national security law. This second edition of National Security Law, Procedure and Practice will be an invaluable resource for judges, policymakers, legislators, oversight bodies, academic experts and students in a variety of legal fields.