In the popular imagination MI5, or the Security Service, is known chiefly as the branch of the British state responsible for chasing down those who endanger national security-from Nazi fifth columnists to Soviet spies and today's domestic extremists. Yet, working from official documents released to the National Archives,distinguished historian Caute discovers that suspicion also fell on those who merely exercised their civil liberties, posing no threat to national security. In reality, this 'other history' of the Security Service, was dictated not only by the consistent anti-Communist and...