The Security Service, also MI5 is the United Kingdom’s domestic counter-intelligence, national security agency and is part of its intelligence machinery alongside the Secret Intelligence Service (MI6), Government Communications Headquarters (GCHQ) and Defence Intelligence (DI). MI5 is directed by the Joint Intelligence Committee (JIC), and the service is bound by the Security Service Act 1989. The service is directed to protect British parliamentary democracy and economic interests, and counter terrorism and espionage within the UK.
The service has had a national headquarters at Thames House on Millbank in London since 1995, drawing together personnel from a number of locations into a single HQ facility. Thames House was, until March 2013, shared with the Northern Ireland Office (NIO) and is also home to the Joint Terrorism Analysis Centre, a subordinate organisation to the Security Service. The service has offices across the United Kingdom including an HQ in Northern Ireland.