BREXIT is turning into a duel of the Dominics. Dominic Cummings, Boris Johnson's combative political adviser, and Dominic Grieve MP, the legally-savvy leader of the pro-European Tories, are right now laying the ground for a confrontation that will test the UK system of government to destruction.

This epic crisis poses great risks, not least of a chaotic Brexit. But it also offers a great opportunity for Scottish nationalists, if Nicola Sturgeon has the determination to exploit it.

Dominic Grieve yesterday told SkyNews that a significant number of Tory rebels are preparing to join Labour, the Liberal Democrats and the SNP this autumn in a vote of no confidence in Boris Johnson's government, if the PM tries to force a no-deal departure from the EU. They will almost certainly win this vote since Mr Johnson has a majority of only one.

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The PM's controversial consiglieri, Dominic Cummings, has of course seen this coming. He's told colleagues that the government's response to the vote of no confidence will be to force a general election – “the people versus politicians” – but delay the election date until after the UK has left the EU on 31st October. That would make a hard Brexit a fait accompli. The health minister, Matt Hancock, says it is now impossible to stop no deal.

Oh no it isn't, says Dominic Grieve, a former Attorney General. In that situation, parliament will simply have to “replace the government”. He is proposing a legislative coup, using parliamentary votes to wrest control from Number Ten and request another extension from Brussels. In effect, Britain could have not one, but two governments wrestling for power as the country crashes out of the European Union on Halloween.

Remainers are resolute, but the Johnson administration has the power of possession. Parliament is sovereign in our system, but it is hard to see how MPs could prise Boris Johnson out of Number Ten. The idea of parliamentary officers, led by the Sergeant at Arms, ordering the Prime Minister out of his new home at sword-point is a compelling image, but it isn't going to happen.

Boris Johnson controls the cabinet: a band of ultra-Brexit ministers who are under oath to carry through Brexit, “do or die”, on the 31st. They will not back down. These Branch Borisians are prepared to go the full Waco and be immolated in the flames of no deal if necessary.

So, is Scotland to be consumed also? When Nicola Sturgeon talked about “material changes in circumstances” justifying a second independence referendum she could scarcely have dreamed of this. A Prime Minister, defying the will of the UK parliament, dragging Scotland to disaster.

The idea of waiting around for a Section 30 order, which will certainly be refused, now seems laughable. Nor is it going to be enough for Nicola Sturgeon to repeat vague promises of a new road map to independence sometime in the future.

The demand from her party, and the independence movement, will be for resolute action by the Scottish Government to defend Scotland from what will be called a Brexit dictatorship.

Increasingly, SNP supporters are asking: what would Alex Salmond do? Well, he wouldn't have started from here, that's for sure. The former SNP leader was a charismatic insurgent, a revolutionary even. He would likely have been leading those rolling independence demonstrations we've been seeing in Scotland over the past 18 months – the largest in Scottish history – which Nicola Sturgeon inexplicably disowned.

Alex Salmond would have used them as a platform, Catalan-style, to launch rhetorical missiles at the Brexit government. You can almost hear him:

Theresa May said now is not the time. Well, Scotland says now IS the time to stand against the Johnson Junta in Westminster. Show this Feckless Franco that Scotland will not be driven off the Brexit cliff by this demeaning diktat.”

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As Brexit day approaches he would call for Scots to take to the streets in an unprecedented show of popular resistance. The Scottish parliament would be convened in emergency session to demand a repeat referendum on independence. He would likely argue that, since parliamentary democracy has been suppressed in Westminster, it must be honoured in Scotland. Holyrood is the only parliament left with the democratic authority to hold a referendum, the mandate for which has been in place since 2017.

Of course, this could all end in tears. The latest Ashcroft poll indicates that support for independence is now over 50 per cent, but there's no guarantee that an unauthorised second referendum would be won. Unionists would boycott it and Number Ten would call it meaningless. However, Salmond might be content to see the result rejected peremptorily by this unpopular Tory government. If nothing else, it could help win the SNP a landslide in the 2021 elections.

But this is to ride the tiger of rebellion, and Nicola Sturgeon does not favour the politics of the street. The First Minister's preference might rather be to lend SNP support to a national coalition government in Westminster, of the kind being proposed by the Guardian columnist, Polly Toynbee.

It is of course theoretically possible for Labour, the Liberal Democrats, Tory rebels and the SNP to put together a crisis administration for the sole purpose of avoiding no deal, or revoking Article 50. However, it seems unlikely that this unelected national government would fly, even if the fractious opposition parties could be persuaded to come together long enough to form one.

MPs may win votes in parliament, but they do not control the civil administration, cannot table legislation and can only briefly seize the parliamentary timetable. Parliament gives authority to a government, but it cannot rule in its place. That requires a general election. Nor is it clear that Brussels is going to ride to the rescue. Ring us when you see sense, was their response to the UK's latest call to drop the Irish backstop.

So, as the Brexit deadline looms, Britain is likely to be in the kind of constitutional turmoil normally associated with unstable African states. Both the Scottish and UK parliaments will be in open revolt against a Prime Minister whose authority rests solely on the strength of his own ego.

Nicola Sturgeon is a cautious lawyer who does not like to live dangerously. But this promises to be the pivotal moment of her political life. And the one thing she cannot afford to do is do nothing.