The question now is, do those members still do that?

For most of my lifetime, the survival of the UK could have been taken for granted, as if geography and some shared history alone could bind together four nations with increasingly divergent identities and interests. Now, the developing political landscape suggests something quite different and that, maybe, a time of reckoning is coming very much closer.

After elections in Scotland and Wales next year, it is entirely possible that Plaid Cymru could govern the latter and the SNP will politically dominate Scotland again. Sinn Fein will still lead the government in Northern Ireland. That would mean three of the four constituent nations of what we still call the United Kingdom might be run by parties committed to ending it. Let’s just consider what that means.

Tom Nairn in his home in Livingston

First, it tells us Westminster’s political and economic model, which is centralised, extractive and dismissive of local democracy, has failed. Decades of austerity, privatisation, and neglect have hollowed out public services across the UK.

As a result, the promise that London knows best has worn thin. The reaction is clear: voters in Wales, Scotland, and Northern Ireland very obviously increasingly believe they could do better on their own, and it would take a very brave Unionist to suggest they are wrong, based on the available evidence.

Second, what this likelihood exposes is the deep economic imbalance that underpins the British state. The south-east of England has hoarded the UK’s wealth, controlled much of the investment in the country and demanded the lion’s share of its new infrastructure.

Meanwhile, the rest of the UK has been left competing for the remaining scraps doled out by the Treasury, through opaque formulas and grudging grants.

What has become clear is that this is not a Union of equals now, if ever it was. It is a fiscal hierarchy that treats English regions and three of the four nations in the Union as colonial-style dependents.

Third, it reveals the moral exhaustion of Westminster politics. Both Labour and the Conservatives cling to an outdated notion of sovereignty which imagines authority flows outward from London rather than upward from the people of the supposedly united kingdom about which they talk but to which they only pay lip service.

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Unsurprisingly, the people of Scotland, Wales and Northern Ireland increasingly reject that, wanting instead competence, dignity and democracy – which none of the English political parties seem able to supply. The consequences of this are not hard to imagine.

If Plaid Cymru were to form a government in Wales, it would not, of course, declare independence overnight. But they would demand real fiscal autonomy, including much greater power to tax wealth, to invest locally and to create comprehensive national energy and transport strategies. That would immediately challenge Westminster’s control of economic policy in the country. Meanwhile, if the SNP, as seems increasingly likely, retain power in Scotland, the question of independence will not disappear.

A new generation of Scottish voters will be emboldened in their demands as a result.

And if Sinn Fein were to lead governments on both sides of the Irish border, as now seems possible, the logic of a united Ireland would become much more difficult to resist. That would create not just a constitutional crisis but an existential one for the UK.

The bigger point, though, is this: the UK’s break-up would not primarily be about identity and nationalism. Nor would it be about economics, as has been the second main focus of the past.

It would now be at least as much about democracy and accountability, and the apparent total inability

of the bankrupt politics of Westminster to provide anything even vaguely approximating to either of those things.

Each of these independence movements has, at its heart, a simple demand, which is the right of each of the three smaller countries within the Union to make decisions for themselves.

The failure of Westminster to respect that desire, to share power meaningfully, or to reform its creaking institutions is what makes the disintegration of the Union not just plausible, but seemingly likely. This is precisely because the prospect of Westminster ever reforming itself without the impact such an outcome might have appears to be vanishingly small.

So what should be done?

First, the UK Government must finally acknowledge that the Union is voluntary. That means recognising the existing, unique and inalienable sovereignty of each nation within it. Doing so in itself would, however, make a mockery of devolution within limits set by London.

Second, there must be a new fiscal settlement as a precursor to whatever might happen next, and this must be one that redistributes both significant revenue-raising powers and spending responsibilities.

Centralised control over money is centralised control over politics. Without economic democracy, political democracy is hollow and Scotland, Wales and Northern Ireland want control now. Third, there must then be constitutional reform, which should not be about tinkering and gestures but be transformational.

Given the current state of play in relations between the nations, if people are to even be faced with a choice about whether to stay in the Union or leave, then England has to accept the need for radical reform so that it might put on the table an option that might induce anyone to stay, rather than to leave as a forgone and inevitable conclusion.

So, the monarchy should go. And the House of Lords. The Commons should be reconstituted to represent a genuine federation of nations and regions, not a population-weighted empire of English seats. Proportional representation would be essential.

Local government must be empowered and not bypassed. And, as noted, fiscal power should be devolved, with the Bank of England, for example, ceasing to solely represent the interests of the City of London. Unless Westminster, on England’s behalf, does all that, it will not even be in the debate on the future of the Union. The fate of that will be determined by its own indifference to effective government.

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Fourth, and most crucially, there needs to be a cultural shift away from the arrogance of Westminster’s exceptionalism towards an acceptance that England itself might need to be reimagined in a post-UK world.

English democracy has never really existed. It might have to be invented.

The end of United Kingdom need not be a tragedy. It could be a renewal, resulting in the creation of a set of co-operative, sovereign democracies, working together on climate, energy, migration, and peace. They could then create a political economy of care rather than control.

Time, however, is short. If the UK continues to presume loyalty, Nairn’s question on the future existence of the Union, posed

nearly 50 years ago, will answer itself, and the whole edifice will fall apart, to the shock of England and the immense relief of most people in Scotland, Wales and Northern Ireland.

The question then is, how long for the UK, then? And the answer is, perhaps not long at all.