Brexit has led to numerous clashes between London and the devolved governments, raising fundamental questions about the very nature of the United Kingdom, in a context where the European Union is no longer available as an ‘external support system’. Michael Keating argues that we need to find new constitutional concepts for living together in a world in which traditional ideas of national sovereignty have lost their relevance.

Since the Brexit vote, there have been repeated clashes between the UK and devolved governments. Some of these concern policy differences, notably over the form Brexit should take. Some reflect the inadequacies of mechanisms for intergovernmental relations. There is an inevitable rivalry between political parties at different levels. Beneath all this, however, are fundamental questions about the nature of the United Kingdom as a polity and where ultimate authority lies, especially after 20 years of devolution.

On the one hand, there is the classic or ‘Westminster’ doctrine, according to which sovereignty resides with the Monarch-in-Parliament. In the absence of a written, codified and enforceable constitution, this is the only foundation of authority. In this view, Westminster has merely ‘lent’ competences to the devolved legislatures, which can be taken back at any time, however politically imprudent that might be. Westminster may not often exercise this power but it provides a trump card in any conflict with the devolved authorities.

This is a powerful doctrine but at the same time an empty one since it rests on a tautology. Westminster is sovereign because, by dint of its sovereign authority, it says it is. The point was illustrated in the debates on the 1978 devolution legislation when an alliance of unionists and nationalists defeated a clause asserting that Westminster remained supreme, the nationalists because they did not want it to be true and the unionists because it was redundant. Westminster sovereignty is a myth, that is a story that may be true or false but works as long as people believe it. When the spell is broken, as it has in recent years, its supporters have to fall back on other arguments. There is a historical argument, that parliamentary sovereignty is rooted in constitutional practice; a normative argument, that in an age of universal suffrage, it really amounts to popular sovereignty; and an instrumental argument, that it allows for powerful and effective government. All are open to question. The historical argument is based on English practice and challenged in Scotland. The normative argument assumes that there is a single UK people with one channel for expression, rather than multiple peoples, the smaller nations having more inclusive electoral systems. The instrumental argument needs to be proven empirically rather than asserted.