In March, the Constitution Unit co-published a new report, Parliament and Brexit, in which some of the UK’s leading academics examine how parliament has managed Brexit to date, and how it might seek to handle the issue in future. Here, Nicola McEwen discusses how the Sewel convention, which regulates the relationship between the UK Parliament and its devolved counterparts, was put under strain by Brexit.

There are four legislatures in the UK, but only one of these is sovereign. The sovereignty of the Westminster parliament remains one of the most important principles of the UK constitution. Each of the devolution statutes made clear that conferral of law-making powers on the devolved institutions ‘does not affect the power of the Parliament of the United Kingdom to make laws’ for Scotland, Northern Ireland and Wales – including in areas of devolved competence. But Westminster’s parliamentary sovereignty is offset by the constitutional convention that it will not normally legislate in areas of devolved competence, or alter the competences of the devolved institutions, without their consent.

That convention, commonly known as the Sewel convention, has become an important principle underpinning UK devolution. It represents a tacit understanding that the devolved institutions, each of which was founded on popular consent in a referendum, have primary democratic and political authority over laws within their areas of competence.

From the outset, the scope of the Sewel convention was ambiguous. The UK and devolved governments have frequently disagreed on the extent to which UK legislation necessitates legislative consent from the devolved institutions. When tasked with determining its status following its inclusion in the Scotland Act 2016 and the Wales Act 2017, the Supreme Court in Miller I concluded that it remained a convention rather than a legal rule, therefore ‘the policing of its scope and the manner of its operation does not lie within the constitutional remit of the judiciary’. The Court thus left it to politicians and parliament to determine the operation and interpretation of the convention. Continue reading →