The Supreme Court's decision to exclude Holyrood from the decision to trigger Brexit only confirmed what we already knew, says Stephen Tierney - that conventions are not laws. However, the proposed Great Repeal Bill is an entirely different matter.
So Holyrood’s consent is not needed to trigger Brexit? Maybe not for now, but in the longer run MSPs will argue that the consent of the Scottish Parliament remains a constitutional requirement before the final decision is made to leave the EU. In fact, while the Supreme Court was clear about Westminster’s powers, it largely ducked the Sewel convention issue.
What do we know for certain? As a matter of law Mrs May cannot trigger Article 50 of the EU Treaty without the consent of the UK Parliament. That means an Act will have to be passed. This is a headache for the Government but not a migraine. David Davis will need to bring forward a Bill but it is now clear that an oven-ready version is already sitting on his desk. MPs will demand a full debate and may even put forward amendments, as might the House of Lords, but the Bill will almost certainly get through Parliament without any cast-iron commitments being made by the Government to detailed scrutiny of the Brexit process. MPs will get another vote at the end of negotiations with the EU, but this has already been promised by the Prime Minister and is likely to be more a ‘veto Brexit if you dare’ threat to MPs than a deferential ‘please may we leave’ proposition.
So no role for Holyrood? This is not so clear. The Supreme Court has said that an Act of Parliament to trigger Brexit will not require, as a matter of law, the agreement of the devolved legislatures. But we knew that anyway. The Sewel convention, by which consent of the Scottish Parliament is needed when Westminster legislates in devolved areas, is exactly that – a convention, not a legal rule. And conventions are about what happens: whether politicians abide by generally accepted constitutional rules even when these are not enforceable in the courts. Westminster will not now accept that a Bill which simply triggers Brexit activates the convention, but there is going to be a much bigger argument over the Great Repeal Bill which will remove the law that took the UK into Europe in the first place. In a potentially important aside, the Supreme Court did acknowledge the convention and affirmed its constitutional significance. The real test for Sewel will come when the repeal bill is on the table. At that point we will see just what role the Scottish Parliament has when the really fundamental constitutional decisions are being made.