This chapter provides a reassessment of competence allocation and exercise under the UK constitution. It shows how the existing allocation needs to be understood through the prism of EU membership, and supports previously provided by the EU’s governance system. In particular, the EU’s commitment to subsidiarity, under which decisions should be taken at the lowest effective level, and its openness to regional concerns, carved out space for the exercise of devolved competence within a system of cooperative multilevel governance. This is in stark contrast to the near autonomous coexistence of the different governments within the UK nation state. As the UK embarks on the process of leaving the EU, its internal distribution of power is subjected to a recentralisation of competence. Informed by the literature on comparative federalism, it argues that there is a need for an effective domestic replacement for the shared competence space previously provided by the EU’s cooperative federalist system of governance. Powerful challenges have come from an attachment to the model of autonomous coexistence of central and devolved levels of government, reinforced by a resurgent principle of Westminster parliamentary sovereignty. Without an effective commitment to shared governance however, the Union’s future is in serious doubt.