The Terrorism Act 2000 abolished all the previous statutory provisions relating to terrorism, apart from a number of specific provisions that continue to exist under the Northern Ireland (Emergency Provisions) Act 1996, the Terrorism (Temporary Provisions) Act 1989, and the Criminal Justice (Terrorism and Conspiracy) Act 1998. The Terrorism Act 2000 defines terrorism in section 1 as:
The 2000 Act contains provisions that allow for certain organizations to be declared as proscribed organizations. It then becomes an offence to be a member of such an organization. The Act also contains detailed provisions as to property defined as being “terrorist property” and the forfeiture of such property. There are detailed provisions relating to the investigation of terrorist activities that grant the police and security services special and extra powers. These include special powers to stop and search, detain, and interrogate those suspected of involvement in terrorist activities.
Like previous legislation relating to terrorism, the 2000 Act was intended primarily to deal with the situation in Northern Ireland. However, since the terrorist attacks on the United States on 11 September 2001 the focus has shifted to the threat of international terrorism. Accordingly, the Antiterrorism, Crime and Security Act 2001 included measures designed to cut off the funding of international terror groups, to ensure the security of the UK's aviation and nuclear power industries, and to restrict access to dangerous substances that could be used in terrorist attacks. More controversially, Part 4 of the Act gave the Secretary of State powers to detain certain classes of foreign nationals for an indefinite period without charge or trial on the basis that they were suspected of involvement in terrorism. This provision required a derogation from the European Convention of Human Rights and was declared unlawful by the House of Lords in December 2004 (A v Secretary of State for the Home Department (2004) UKHL 56,  2 AC 68). The Prevention of Terrorism Act 2005 repealed these so-called Part 4 powers and replaced them with a system of Control Orders, under which the Secretary of State can apply to the courts for an order imposing various restrictions on the movements or activities of named individuals (whether they are UK nationals or not). If the order is granted, then the decision of the Minister is automatically subjected to judicial review. However, there is no obligation to disclose the evidence on which the decision was based either to the person made subject to the order or to his legal counsel of choice. In June 2006 the High Court quashed six of the control orders then in force, as being contrary to the Human Rights Act. This decision was reversed by the House of Lords, which nevertheless ruled to limit curfews to 14 hours in 24.