	Introduction

This is a comparison of the law of the United States (U.S.) and United Kingdom (UK) relating to the authority to investigate terrorism. Many of the differences can be understood in light of the reach of the Fourth Amendment to the United States Constitution. The use of these methods are subject to a lengthy and complex legislative regime contained in the Regulation of Investigatory Powers Act 2000 (RIPA), the Police Act 1997, and the Intelligence Services Act 1994; and supplemented by the protections in the European Convention on Human Rights. In the United States, a court order is required for the lawful interception of communications in most circumstances and can be obtained either under the Electronic Communications Act (Title III) or the Foreign Intelligence Surveillance Act (FISA).
This is a comparison of the laws of the United Kingdom and of the United States that govern criminal and intelligence investigations of terrorist activities. Both systems rely upon a series of statutory authorizations: in the case of the United States primarily the Foreign Intelligence Surveillance Act and the Electronic Communications Privacy Act; in the case of the United Kingdom, the Regulation of Investigatory Powers Act, the Police Act, the Intelligence Services Act. Among other differences, the U.S. procedures rely more heavily upon judicial involvement and supervision, while those of the UK employ other safeguards. The UK procedures afford greater latitude to arrest, detain and supervise suspected terrorists than those available in the United States.