MI5

British Security Service. Originally organized in 1909 to counter German espionage, in 1931 it assumed wider responsibility for assessing threats to national security, including communist subversion and subsequently fascism. Today the Security Service Act (1989) forms its statutory basis. As Britain's domestic-security intelligence agency, its purpose is to protect the country against threats such as terrorism, espionage, and subversion. Since the passing of the Security Service Act (1996), its role has been expanded to include supporting law-enforcement agencies in the field of organized crime.