LEGISLATIVE consent may sound like another of those tiresome lawyer’s phrases; it’s anything but. Lack of it could stall Brexit, trigger an independence referendum or even break up the Union.

Legislative consent is what used to be called the Sewel Convention, under which the Scottish Parliament has a right to vote on actions of Westminster that impinge on its powers. Today, the UK Supreme Court will address whether or not Holyrood has a right of consent on Article 50, triggering Brexit.

The UK Government is adamant that it should not, and that the Scottish Parliament has no right to interfere. Anyway, the constitution is reserved to Westminster. Advocates of legislative consent, including the Scottish Government, argue that Holyrood certainly should have a say because Brexit will massively affect Holyrood’s powers. Under the Scotland Act 1998, Scottish legislation has to be in accordance with EU law, and this will end when the European Communities Act is repealed.

Moreover, in the Scotland Act 2016, the Sewel Convention was supposedly put on a “statutory basis”, as part of the post referendum “vow” on entrenching Holyrood’s powers. Most people believed this meant that there was now a legal obligation for Holyrood to give its assent to changes to its powers. But no.

The UK Government had inserted a weasel word into the Act. It says that “Westminster will not NORMALLY legislate with regard to devolved matters without the consent of the Scottish Parliament” Since Brexit is not “normal” then legislative consent doesn’t apply. Ha, ha – Scots should have read the act more carefully.

The Supreme Court is expected today to uphold the earlier High Court decision that MPs in Westminster should have a vote on Article 50. That will be a landmark constitutional ruling. But the “Enemies of the People”, as the Law Lords were described by one newspaper, are less likely to argue that Holyrood has a right to legislative consent. Why should they? The Scotland Act may have been disingenuously drafted – but that is a political matter, not a legal one.

Nicola Sturgeon has promised to hold a vote on Article 50 whatever the Supreme Court says or doesn’t say today, though this would have no legal force. She insists Scots voted by a margin of two to one to remain in the European Union and cannot be ignored. But Theresa May has already ignored the Scottish Government’s call for Scotland to be allowed to remain in the single market after the rest of the UK leaves it.

Will all this make Scottish voters more keen on a referendum on independence? It’s difficult to say, since these legal disputes go over most people’s heads. But the status of Holyrood is important.

Many Scots believed that, under the Scotland Acts, Scotland was more than just a region and that its parliament exercised sovereignty over the areas of its own competence. This is an illusion that has been rudely shattered.

Brexit will also deprive Scots of European Union citizenship which they have enjoyed since Maastricht in 1993. EU citizenship gives Scots the rights of free movement anywhere in Europe, representation in the EU Parliament, and freedom from discrimination on grounds of nationality. These are significant rights, which many Scots will be reluctant to give up.

No-one doubts that the Scotland Act 2016 will have to be revisited after Brexit. The 1998 Act will have to be amended to remove the obligation that all laws be in accordance with Brussels. Optimists believe this will deliver the “Brexit dividend” of more powers over agriculture and fisheries. But it’s more likely to confirm Scotland’s subordination to Westminster, even in the areas of devolved competence. Certainly, no-one will believe any promises about Holyrood’s powers. It’s beginning to look as if, post-Brexit, the UK Union itself is being strengthened and turned into something more monolithic than hitherto.

In the months before the 2014 referendum, there was much talk about how Scotland had become, to all intents and purposes, part of a federal UK, and that independence wasn’t necessary any more. We can safely lay that argument to rest now. Under federalism the powers of the states are clear and permanent; they exercise sovereignty in those areas. Brexit has made clear that the Scottish Parliament does not exercise sovereignty, relative or absolute.

Scots must now accept their reduced status as a region of the UK – an important one, but a region nevertheless.

The only alternative now is full independence.