KEZIA Dugdale is right about one thing: the Scotland Act 2016 lies in ruins after Brexit and the changes that it will bring to Holyrood’s powers. However, in reviving former prime minister Gordon Brown’s call for “federalism in the UK” she is trying the patience of Scottish voters. After the revelations in the Supreme Court Article 50 hearings, it’ll be a hard job persuading Scottish voters to believe anything any UK prime minister, commission, or so-called vow says about federalism ever again.

Federalism, in the Scottish context, means that the Scottish Parliament is regarded as a permanent institution and that the UK Government cannot abolish it or interfere with its powers. This was essentially what Mr Brown promised in his barnstorming speeches in the dying days of the 2014 independence campaign. He also promised enhanced economic powers.

Federalism may not have saved the day for the Union and there was a certain vagueness about how a federal arrangement would work in a country with no written constitution where one “state”, England, is so much larger than the others. But no Scottish voter could have been in any doubt. Following the “vow”, devolution would be unalterable and the powers of the Scottish Parliament could not be revoked without consent.

This was made explicit by the cross-party Smith Commission whose recommendations were enacted by the 2016 Scotland Act. Its top lines, as explained by the Scottish Parliament Information Centre, were, first: “The UK legislation will state that the Scottish Parliament and Scottish Government are permanent institutions”and, secondly: “The Sewel Convention under which the UK Parliament will only legislate on devolved matters with the agreement of the Scottish Parliament, will be placed in statute”. That phrase “placed in statute” means that it becomes the law of the land. At least that’s what Scottish voters and MSPs thought it meant.

We now learn that this is not what the UK Government meant. The Advocate General, Lord Keen, speaking for the UK Government in the Supreme Court, said this “statutory footing” was merely a form of words. Irrespective of the Scotland Act, Sewel was just a “self-denying ordinance” and not in any way binding. Moreover, Holyrood’s agreement to changes in its powers was only required in “normal” times. Brexit is not normal. Ergo: you’ll have had your legislative consent.

Some of us noted during the passage of the Scotland Act that Westminster’s ultimate sovereignty was not altered by it: that it “does not affect the power of the UK Parliament to make laws for Scotland” as in the original 1998 Scotland Act. But most of us also assumed a measure of good faith. The Scottish people were certainly led to believe that Sewel would be binding in future. Most conventions are; it is only a “convention” that the monarch passes into law legislation voted for by the UK Parliament. Yet that is about as binding as you can get.

The Lord Advocate, James Wolfe, argued for the Scottish Government yesterday that the 2016 Act converted Sewel “from a convention into a rule of law”. Otherwise, why did Parliament put it in legislation? This, he said, meant that the Scottish Parliament has the legal right to pass a legislative consent motion on Article 50 because Brexit fundamentally affects the powers of Holyrood on everything from employment to the environment. The Law Lords didn’t sound entirely convinced by the Lord Advocate’s rather halting speech. They spent rather a long time debating what “normally” means.

The issue is much broader than Article 50. The UK Government’s argument makes clear that all the talk of “entrenching” Holyrood and its powers in the wake of the independence referendum was so much hogwash. Federalism was not remotely on the agenda. It suited ministers to allow it to appear as if the Scottish Parliament had that constitutional certainty. In reality, the Scottish Parliament is just a here-today-gone-tomorrow institution that can be overruled and, in theory at least, abolished by Westminster as it sees fit.

If so much of what has been said since 1998 amounts to weasel words, then who now is going to buy Ms Dugdale’s call for a new constitutional convention to map out a federal future for the UK? The Scottish Labour leader has a a credibility gulf as wide as the Act of Union. There’s not even any guarantee that London, Wales or English regions would participate in Ms Dugdale’s convention which, she says, has to be UK-wide and would not be put to any vote of the Scottish people alone.

This is unfortunate as much of what she was arguing in her speech yesterday was constructive. She called for Holyrood to have powers over employment and the minimum wage. She in similar vein in July: “There was a possibility that Scotland could retain its place in both the UK and in the EU through ... a potential federalist solution.” This is not a million miles from what Nicola Sturgeon has been calling for.

The First Minister also wants a unique constitutional arrangement for Scotland, allowing it to remain in the single market when Britain leaves the EU, a federalist argument. It implies that Scotland could remain part of the EU and the UK, which could only happen if Scotland had a clearly defined, “entrenched” constitutional status in which its powers were defined and made irreversible.

Some might wonder why the UK Government has chosen to take such a regressively centralist approach to legislative consent. Why revive all the suspicions of Perfidious Albion? Even the Lord Advocate accepted that, while the Scottish Parliament had the right to be consulted on Article 50, it was also clear that Westminster could overrule it. Why go to the wall over a legislative consent motion MPs can vote down in the House of Commons?

But the UK Government is arguing against any parliament having the right to a vote on Article 50. Theresa May had tried to trigger Brexit using the pre-democratic powers of Royal Prerogative, bypassing Parliament. She could hardly concede a power for Holyrood to have a vote on Article 50 when she was denying one to Westminster.

The UK Government might also worry that Westminster might decide not to overrule the legislative consent motion from Holyrood. Most MPs are Remainers and they might question whether it’s wise to risk another independence referendum by voting down the Scottish Parliament.

Such a confrontation might bring to pass another of Ms Dugdale’s proposals: a new Act of Union. That looks like where we’re heading even without a constitutional convention. But she had better believe that any new act would be based on the repeal of the 1707 act and would make unequivocal the demand for an entrenched, sovereign Scottish Parliament. In other words: independence.