Most political crises come from nowhere and take everyone by surprise. But some have been staring us in the face for months, years even, and they still hit us unprepared. Such is the constitutional crisis over Scotland’s place in the Union.

We’ve known for months that the independence-supporting parties were likely to win a big majority in the 2021 Scottish parliamentary election. But it is only now, as we’ve seen it happen, that the potential crisis has become actual.

The UK Government insists there is no case for another referendum on independence because we had one in 2014. Boris Johnson has even suggested that the gap for Indyref2 should be the same as between the first and second referendums on Europe: 36 years. But this has been a holding position and is no longer sustainable. Ciaran Martin, the former UK Cabinet Office civil servant who oversaw the 2014 referendum, says this rejectionism is an offence against democracy itself. If the independence parties win another majority, he said last month, “there is no legitimate justification on which to resist a referendum”.

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It is true there were other issues in this election campaign besides the referendum: education and the pandemic for starters. But no-one in Scotland could have been in any doubt about what they were voting for on Thursday. When they placed their crosses on the SNP and the Greens, they were voting emphatically for Indyref2. Scottish voters must themselves now take responsibility for their actions. The very size of the turnout has upped the constitutional ante.

The Scottish Tory leader, Douglas Ross, claimed that Nicola Sturgeon was planning an illegal “wildcat” referendum. That is untrue. She has always said that the only referendum she would agree to is a constitutional, legally-binding one authorised by Westminster under a Section 30 Order. This is for a very good reason. Only such a referendum would be regarded as legitimate by other countries – especially the European Union, which the SNP is eager to rejoin. Only a legally-binding referendum would put the result, as she put it, “beyond doubt or challenge” in the eyes of the world.

Which doesn’t mean she will simply accept the Westminster veto. Ms Sturgeon made clear in the Channel 4 leaders’ debate that she intends to go to court herself. She will ask the Scottish Parliament to pass a referendum bill and then defy Boris Johnson to reject it. Assuming he does, the Scottish Government will then challenge this ruling in the courts. I’m not entirely sure this will succeed, and I’m not entirely sure she thinks it will either. The Supreme Court would ultimately rule on the matter, and it seems unlikely that the United Kingdom’s highest court would actively support the dissolution of the United Kingdom.

But that isn’t really the point. Court action would be constitutional theatre designed to increase the moral pressure on Boris Johnson to offer a plausible referendum timetable. There was speculation last month that he might actually do this. Ministers had, it was reported, considered holding a snap referendum to catch the SNP unawares.

Support for the SNP may remain stratospheric, but support for independence has been waning somewhat. Nicola Sturgeon has had difficulty explaining the new border and currency issues that arise with independence post-Brexit. So why not put the question now, while the SNP is on the back foot?

I don’t think there’s much risk of this happening. Boris Johnson may have won the Brexit vote, but he is very wary indeed of referendums. He saw what happened to his predecessor, David Cameron, who thought the 2016 referendum would be a walk-over for Remain. The 2014 referendum was a near-death experience for the British state. Referendums are highly unpredictable, and rarely just about the narrow question on the ballot paper.

Indeed, a second Scottish independence referendum could easily turn into a referendum on Boris Johnson himself – a figure who is profoundly unpopular in Scotland. The Scottish Conservatives barred him from appearing in the election campaign, even though the PM had said that “wild horses” couldn’t keep him away.

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We have heard much about the Government’s plans for massive investment in Scotland on roads and rail links, even a bridge or tunnel to Northern Ireland. But such pork-barrel initiatives are unlikely to answer the fundamental question. If the UK Government is to repeatedly reject the clearly expressed will of the Scottish people to hold a referendum, how can it reasonably claim to be a democracy? Continuing to reject it would transform the Union from being a partnership of nations into a coercive union, based on legal force.

Piecemeal reform, such as the Smith Commission in 2014 that tinkered with tax powers, and gave a mendacious assurance that the Sewel Convention was inviolable, will not do. There has to be a recognition in Westminster that Scotland is now in charge of its own destiny. I believe there are ways to achieve this and retain the only union worth saving: one that is a free and equal partnership of nations.

The devolution era is over. Power devolved is power retained, and events since Brexit have confirmed the wisdom of that dictum. The federal boat, however, has also sailed. England would never agree to the upheaval involved in creating the constitutional paraphernalia of federalism: regional parliaments, a federal executive, a president of the UK. They are quite happy with the Parliament they’ve got. What might be possible is a form of asymmetrical federalism that the late Labour First Minister, Donald Dewar, used to call “independence in the UK” and the SNP called “fiscal autonomy”.

All tax and spending powers could be devolved to Scotland, with Holyrood sending back a percept, a kind of fee, for common services like defence and currency. This would end the Barnett Formula and give full economic responsibility to Holyrood, but retain the social and cultural links with the rest of the UK. It would largely fulfil what was envisaged by the SNP’s 2013 Independence White Paper: a “new UK” with a common currency, borderless trade with England, and the retention of UK institutions like the Crown and BBC.

This would be a radical departure, however, not dissimilar to the way countries like New Zealand and Canada acquired quasi-independence in the 1930s in the sterling area. The evidence is pretty clear that England, which following Hartlepool is becoming more Tory and more nationalist, would not object. It would mean Scotland taking charge of the money issue and ending what has been called Scotland’s “dependency culture”.

For their part, Scottish nationalists are beginning to realise that independence is no walk in the park now that Britain is out of the EU. No-one wants a hard border with England, but one is now inevitable.

Independence in the UK would create a new Union held together not by legal constraint, but by consent. I have no idea whether Boris Johnson has the will or the imagination to seize this opportunity. I rather doubt it. But even he must realise that doing nothing is no longer an option. As the prince said in The Leopard, “everything must change in order to remain the same”.