Numerous allegations of abuse of power have been made against the domestic security intelligence agencies in the United Kingdom - police special branches and MI5. These include the improper surveillance of trade unionists and peace activists, campaigns of disinformation against elected politicians and, most serious of all, the summary shooting of people believed to be engaged in political violence. Although in recent years far-reaching inquiries have been conducted into similar agencies in other liberal democracies, and the end of the Cold War has brought dramatic change to security agencies in Eastern Europe, the UK agencies have remained aloof from anything more than marginal organisational change. 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. This provides, first, a systematic discussion of what is known about the operations of security intelligence agencies in liberal democracies and, second, an agenda for research into the UK agencies, including: the ambiguous nature of their mandate regarding 'national security', 'subversion' and 'terrorism'; the ways in which the agencies penetrate society and what they do with the information they gather; internal organisational questions such as recruitment and culture; the extent to which the agencies are controlled by ministers; and how the agencies' activities might be overseen by outside political bodies such as parliamentary committees, and by citizens in general.