This chapter will examine national security and the limits of judicial protection in the United Kingdom (UK). 1 National security is a matter reserved to the Westminster government and Parliament. As we shall see, it is an area subject to the pervasive protection of secrecy, an aspect I have addressed in previous publications. 2 An eminent judge and jurist Sir Stephen Sedley has written that the UK’s security establishment has arguably become a fourth power of the state. 3 The democratic and justice ideals of a liberal democratic state such as the UK have to come to terms with institutions which are of long antiquity in British governance but that have escaped any form of democratic and justice oversight until comparatively recently. In a democratic system this posed particular difficulties in a country like the UK which has no written constitution. The overriding symbol of power and legitimacy in the UK is the Crown. The Crown in Parliament is the sovereign law maker. Unlike a written constitution, the ‘Crown’ does not provide the ultimate source of public powers. Rather ‘[p]ower in the United Kingdom flows up from the state’s component elements, making the Crown its receptacle [and its cover] 4 , not its source’. 5 I think this chapter will illustrate Sedley’s concerns that ‘National security furnishes a series of critical instances of the difficulty of reconciling the modern state with the rule of law’. 6