The union of Scotland and England was the founding act of the UK in 1707, and consensually agreed between two sovereign parties. Scotland was never a colony of England and post-union retained considerable autonomy, including its distinct and separate legal and education systems and Church. As a result of the 1707 union, the UK Parliament (which was not simply the English Parliament enlarged) came into being. The doctrine of unlimited parliamentary sovereignty is not accepted by everyone in Scotland, where there exists an alternative Scottish tradition of popular sovereignty, and the belief that Scotland’s place in the UK Union rests on its consent. Since devolution in 1998, Scotland has developed some progressive constitutional forms, as well as more pro-European inclinations that challenge the unitary constitutional approaches of London. Brexit, however, has placed the UK union under strain, and there have been demands for a second Scottish Independence referendum. Surprisingly, despite the threat of Scottish independence, there has been little debate about what the ‘Union’ or ‘Britain’ is or should be.

The referendum vote in 2016 to leave the European Union (Brexit) and the process for its implementation have had a significant impact on the devolution framework, and in particular on its legal mechanisms for ensuring harmonious relations between Westminster and the devolved legislatures, and for resolving conflicts between them. Focusing on the Miller and Scottish Continuity Bill cases, this chapter highlights the problems arising from the use of the mechanisms established in the devolution settlements, primarily designed to ensure that the devolved legislatures do not act ultra vires, for the legal resolution of competence conflicts between both orders of government. Taking into consideration the significant role that the courts play in federal or quasi-federal systems by providing an independent and balanced interpretation of the constitutional framework, this chapter reflects on the effectiveness of these mechanisms in the UK system and argues that, in the light of recent developments, they need to be reformed to enable the access of the devolved institutions to the courts in this context.