Brexit aimed to restore sovereignty to the United Kingdom. That rested on an interpretation of the UK as an internally integrated and externally bordered sovereign state. Another interpretation is that the UK is a plurinational union, in which the issue of sovereignty is contested. Devolution in 1999 left this issue in abeyance, while membership of the EU provided an external support system. Brexit removed this external support and resulting territorial tensions are exacerbated by the fact that majorities in Scotland and Northern Ireland opposed it. There have been three responses: to reconstitute the United Kingdom as a unitary state; to fragment it into its constituent parts; and to seek a differentiated Brexit. Only Northern Ireland has been granted such an exception, at the insistence of another Member State.

MICHAEL KEATING, (2021) Taking back control? Brexit and the territorial constitution of the United Kingdom, Journal of European Public Policy, DOI: 10.1080/13501763.2021.1876156, (2021)