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.