For much of the twentieth century, relations between Britain and the Soviet Union were defined by mutual hostility and distrust. From the Bolshevik Revolution until the end of the Cold War, the British establishment was deeply concerned about Soviet-inspired subversion, and secretly monitored thousands of its own citizens due to their real or perceived links to communism, the Soviet Union or both. Enemy of the State reveals how Britain's intelligence services carried out mass spying operations on the grounds of protecting democracy. Using phone taps, hidden microphones, mail interception and covert break-ins, they investigated trade unionists, scientists, politicians, actors, anti-nuclear and anti-apartheid protesters, and more. But the culture of secrecy permeating British institutions has meant that the extent of these activities is little known. Drawing on recently declassified files from the British government and MI5, Oliver Price argues that while communism gained little traction in domestic politics, fear of left-wing radicalism led to the widespread monitoring of individuals and political groups--many of whom posed no threat to the British state. Britain was long considered a country in which 'political policing' was resisted. But Price shows how the tumultuous events of the last century reshaped official attitudes and normalized surveillance.