“Petulant..vulgar...immature attention-seeking”. The UK press were largely united in condemning the SNP's parliamentary walkout. “A stunt”, they called it. Well, of course it was a stunt – but such theatrics are as much a part of Westminster tradition as Black Rod.

You don't have to go back to Charles Stewart Parnell's use of parliamentary disruption to promote Irish Home rule in the 19th Century. There was the then Labour MP Denis Canavan crying “strangers in the gallery” back in 1987 after the Tories had been routed in Scotland. Even the ultra-respectable Donald Dewar appreciated the importance of political theatre and led a walk out of MPs shortly thereafter. And of course we had Alex Salmond's disruption of the 1988 budget speech.

And the point is that it works. Does anyone seriously believe that, had it not been for this “stunt", that the Sewel Convention and the Scotland Act would have received a smidgeon of the attention it did last week? It led the BBC news for the first time, was examined at length in Channel 4 News, and was a hot topic on Question Time. The Guardian even ran an editorial on the issue of consent which, typically, condemned the walk out while saying it was actually justified.

And of course it was. Having the Scottish parliament's powers stripped away was bad enough, but leaving only 15 minutes to debate this was provocation too far. The UK government's view, echoed in a screamingly pompous Spectator comment on the walk out, is that no one in Scotland is interested in the constitution. ”It's anarchy up there” it teased, “Elderly ladies are smashing up tearooms and Church of Scotland ministers have started lamping passing policemen with bottles of Irn Bru”.

Well, the SNP got the last laugh as 5,000 new members signed up to the party within the next 24 hours. The former editor of the Daily Record, Murray Foote – the man who actually drafted the infamous Vow - then declared that he was now a supporter of independence. The combination of losing EU citizenship and seeing Holyrood demoted drove him over the edge. One suspects many more No voters from 2014 are having similar second thoughts – even if they can't thole the thought of another referendum right now.

People are beginning to understand why the parties in the Scottish parliament united – bar the Tories – to refuse legislative consent to the Brexit bill. It is because the UK government has not the least interest in respecting the fundamental principle of devolution: that Westminster should only legislate for Scotland with the consent of the Scottish parliament. It's not just about fish, farming and food labelling, important though these matters are. It is about the power relations between Scotland and Westminster. Parliamentary politics is all about precedent: once it is established that Westminster can dictate to Holyrood, “whenever there is disagreement” as David Mundell put it baldly in his statement, then that will set the ground rules for the future.

It is also about whether Holyrood continues to be a proper parliament with primary law-making powers, or reverts to the status of a city council. As the Brexit insider, and Times journalist, Tim Shipman, put it last week, with inadvertent candour: “why should Scotland be regarded as any more important than Manchester?”. The answer is because Scotland is one of the two nations of the Union, which Manchester is not, and because it has had its own parliament for domestic affairs since 1999. That is called Home Rule. Anyone with the slightest understanding of the UK constitution, and the history of Ireland, should surely understand why this is important. Yet, the vast majority of Tory MPs – and I fear many Labour ones – are condemned to repeat the mistakes of the past.

This was exactly the kind of dismissive talk about devolution that led to the Scottish Tories being wiped out in the 1997 general election. They had been insisting that “only 1000 people in Scotland care about the constitution”, as Michael Forsyth put it. That was barely a year before the landslide in the 1997 devolution referendum, when three out of four Scots voted for the creation of the Scottish parliament. They may not smash windows and burn effigies of Theresa May, but that doesn't meant that Scottish voters are uninterested in the fate of Holyrood, even though they don't necessarily engage with the constitutional hermeneutics of asymmetrical federalism.

The Sewel convention is the rule that Westminster should not legislate in areas that are the Scottish parliament’s responsibilities without consent. As a reward for voting No in 2014, Scots were promised that this would be put on a statutory basis - a law not a mere convention. This was soon undermined by the insertion of the word “normally” before “legislate”in the 2016 Scotland Act – a cynical exercise in parliamentary draftsmanship. Now all pretence that Holyrood is a co-equal partner in domestic legislation is being openly discarded. As Mundell put it, in a remarkable statement, “Scotland is not a partner in the UK, it is part of the UK”.

It is abundantly clear that Brexit is all about rolling back Scottish home rule. It is incompatible with the creation of the new unitary British state, envisaged by the no-imperialist romantics of “Global Britain”. It is naïve in the extreme to believe that after seven years, in which the UK government will exert a kind of colonial authority over the Scottish parliament, that the powers will be returned and all will be as before. Once it’s gone, it’s gone.

The EU (Withdrawal) Bill will now become law, though technically it cannot get the Royal Assent without the consent of the Scottish parliament, which has been withheld. This can probably be resolved by another quick vote when the Withdrawal Bill comes back from the Lords for its final stages. Regrettably, since Labour has decided to tacitly endorse the power grab – it abstained on the vote on Clause 11/15 – there is little chance that this can now be prevented. Similarly, Labour MPs will likely ensure that the government prevails in the forthcoming trade bills in July, from which the Scottish parliament will also be withholding consent. Why Labour is so reluctant to challenge Theresa May on her approach to devolution is a mystery. They claim it is to support Wales, who have accepted the power grab clause.

But Wales is not Scotland, and the consent issue is central to the original Scotland Act, which was the brainchild of the celebrated Labour Scottish Secretary, Donald Dewar. Moreover, Labour MSPs voted in Holyrood to refuse legislative consent to the very Bill which their UK MPs are now helping to impose on Scotland. This may make sense to someone, but it is politically dyslexic. Home Rule should be Labour's political property, it's unique contribution to Scottish political culture. Why throw it away to help a UK Prime Minister, who is on the ropes and on her way out, deliver a discredited Brexit bill that makes the case for Scottish independence by confirming Enoch Powell’s famous claim that “power devolved is power retained”.