To the extent that the UK's decision to withdraw from the EU can be interpreted as a reassertion of the classic ideas of Westphalian sovereign statehood, it questions the relevance of constitutional pluralism as a resolutely ‘post-sovereign’ model of relations between state administrations and their supranational counterparts. This contribution will therefore examine the usefulness and relevance of the idea of constitutional pluralism after Brexit. It looks at the various features and relationships affected by the Brexit process analysing the relevance of constitutional pluralism to each relationship pre- and post-Brexit, concluding that, whereas Brexit clearly affects the different relationships involved, constitutional pluralism can and will remain relevant to EU/UK relations as well as within the EU, well into the future.

The explosion in the literature on global constitutionalism in recent times has come at the cost of ever more, and more diverse, definitions of the concept of constitutionalism. The state of the current debate can therefore be characterised, conceptually speaking, as a ‘constitutional cacophony’. This cacophony is the inevitable result of the ‘problems of translation’ in importing the state-based concept of constitutionalism to the global level. This article attempts to counter suprastate constitutional scepticism borne of these problems of translation and resulting cacophony by revisiting the concept of constitutionalism itself through the lens of legitimacy. Arguing that legitimacy provides both a key element of the concept of constitutionalism as well as a common denominator for the application of constitutionalism both at the state and suprastate levels, it develops a conception of ‘constitutionalism as legitimacy’ as a way of vindicating the role of constitutionalism in the context of global governance. It presents constitutionalism as a discursive ‘mixed’ form of legitimacy entailing both factual and normative components involving a blend of liberalism and republicanism. These theories are then reworked into a framework of reasons for the legitimacy of an authority centring around its origins, its aims and its methods. Tracing the relationship between constitutionalism and legitimacy in this way brings harmony to the global constitutional cacophony and allows for a plausible ‘translation’ of the concept of constitutionalism between the state and suprastate levels allowing for an effective ‘mapping’ and ‘shaping’ of legitimacy in global governance which is illustrated by reference to the legitimacy crisis surrounding the United Nations Security Council’s ‘war on terror’.