Numerous allegations of abuse of power have been made against the domestic security intelligence agencies in the United Kingdom such as police special branches and MI5. These include the improper surveillance of trade unionists and peace activists, campaigns of mis-information against elected politicians and even the elimination' of people believed to be engaged in political violence. Drawing on extensive foreign material and making use of the social science concepts of information, power and law, this book develops a framework for the comparative analysis of these agencies.