MI5

The Security Service, commonly known as MI5 (Military Intelligence, Section 5), is the United Kingdom's domestic counter-intelligence and security agency and is part of its intelligence machinery alongside the Secret Intelligence Service (SIS; also known as MI6) focused on foreign threats, Government Communications Headquarters (GCHQ) and Defence Intelligence (DI). All come under the direction of the Joint Intelligence Committee (JIC). The service has a statutory basis in the Security Service Act 1989 and the Intelligence Services Act 1994. Its remit includes the protection of British parliamentary democracy and economic interests, counter-terrorism and counter-espionage within the UK. Although mainly concerned with internal security, it does have an overseas role in support of its mission.

• http://en.wikipedia.org/wiki/MI5