The United Kingdom (UK) battles the threat of domestic terrorism since the 1960s, primarily based on the Irish Republican Army. The last few years, the threat of terrorism based upon the "occupation" of Northern Ireland by the UK has waned, and the threat radical Islamic based terrorism has moved to the fore-front. It argues that the United Kingdom is less concerned with restrictions on civil liberties, for example, in combating terrorism, as unlike the United States, the United Kingdom lacks constitutional protections and a delineation of civil liberties in the form of a constitutional bill of rights. The British courts lack the ability to hold acts of Parliament to be unconstitutional, unless a dimension of EU law is raised in the case. The most important source of constitutional law in the UK stems from statutory law enacted by the Parliament. US argues that "constitutional law" is more imprecise, given the fact that it must be gleaned from multiple sources.