How, in a democratic state, can the competing interests of the need for national security and the demand for open government be reconciled? Should Security Services have a legal obligation to report their activities and should their members be held liable for exceeding the powers bestowed upon them by Parliament? These questions have taxed governments and academic commentators for generations until now. The early 1990s have witnessed an unprecedented change in public opinion and governmental attitude away from the extreme levels of secrecy and mystery which have traditionally enshrouded the Security Services. In this searching analysis, two leading constitutional lawyers shed light on the legal powers and basis of this murky area of government, comparing the accountability of Britain's Security Services with the very different situations in Canada and Australia. The authors question whether we still need, or should tolerate, the level of secrecy together with all the possibilities for misuse and abuse of power which accompany it in this authoritative study of the constitutional and legal position of the Security Services in Britain.