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Whatever the Scots decide on Thursday, this is only the start of a formidable constitutional convulsion. The question to be resolved this week is what its character will be.

Today, the Prime Minister will deliver his closing argument in a speech in Aberdeen, intended to persuade those inclined to back independence that this is not a protest vote but a one-way ticket. “There’s no going back from this,” Cameron will say. “No rerun. This is a once-and-for-all decision. If Scotland votes yes, the UK will split, and we will go our separate ways forever.”

As senior sources emphasise, this would be divorce, not a trial separation. There will be no alimony in the form of a shared currency, only a row over who gets custody of the nuclear subs and the national debt. If Scotland votes for independence, Scotland’s First Minister Alex Salmond and British Prime Minister David Cameron will be obliged on Friday morning to promise neighbourly friendship, a geopolitical Gwyneth Paltrow and Chris Martin embarking upon “conscious uncoupling”. But — rhetoric aside — the split will be anything but amicable. The only message to emerge with any clarity from recent surveys is that the nation of Scotland is genuinely confused about its future.

In the past few weeks, its answer to a question of pitiless simplicity has been that of Vicky McPollard: Yeah-but-no-but-yeah-but-no. The Survation poll recently put Unionists eight points ahead of the Yes campaign. But an ICM poll, which shows support for independence now eight points ahead, cannot, and will not, be ignored.

Cameron is right to warn the Scots that the leap from the precipice is not a bungee jump. Officially, the Coalition and Labour have nothing to say about contingency planning for life after a “Yes” vote. But beneath the surface of constitutional calm, the webbed feet of the political strategists and wonks are paddling crazily.

Labour, for instance, is determined that the transition to independence should be overseen by a cross-party body. “I have never seen so many strategy papers in my life,” as one source puts it. And rightly so. If the Scots vote for independence, Ed Miliband will face a brutal dilemma. At present, Labour holds 41 of the 59 Scottish seats at Westminster. Assume, for the sake of the argument, that Miliband retains them in the general election, which he wins with only a narrow majority. Those MPs would be obliged to leave the Commons — forever — on March 24, 2016, already pencilled in as Independence Day.

What if their departure drastically reduced or even destroyed Labour’s putative majority? More to the point: How would Miliband govern with any credibility between May 8, 2015, and Dignitas Day for the Union? These are hypothetical questions. But they may not be hypothetical for very long.

As for Cameron, all talk of his defenestration is just another variant upon the conversation that Tory MPs have been having with one another for a quarter-century: why is our leader unworthy of us and how can we get rid of him (or her)? The selection of Boris Johnson as Tory candidate in Uxbridge and South Ruislip on Friday night, and of Giles Watling in Clacton last Thursday, removed at least one (already remote) possibility from the spectrum of threats: Namely, a letter signed by a sufficiency of backbenchers to Boris, persuading him to stand in the Clacton by-election on October 9, affording him an immediate route back into the Commons, unsullied by the Coalition, loved by plotters and pundits alike, available to replace Cameron swiftly.

It is to Boris’s credit that he has steered clear of this nonsense. If Britain dies on Thursday — what an amazing clause to write — the last thing these fractured islands will need is the resignation of the PM pouring petrol on the pyre. Naturally, a “Yes” vote will cast a long shadow over Cameron’s premiership as, in a different way, Irish Home Rule did over William Gladstone’s. It is absurd to blame the PM for the referendum itself: Salmond would have held his own plebiscite had he not agreed to co-operate in the exercise. The PM’s error of judgment was his evident confidence that the referendum would perform its ancestral constitutional role, as envisaged by the great jurist, AV Dicey (1835-1922). Obsessed by preventing Irish Home Rule, Dicey judged the referendum to be “the people’s veto” and a brake upon “a fundamental change passing into law which the mass of the nation do not desire”. This is precisely what happened in May 2011 when the electorate, to the bitter disappointment of Cameron’s Lib Dem Coalition partners, roundly rejected a change to the voting system at Westminster.

In Scotland, the “No” campaign’s apparently robust lead, secure for many months, suggested to No 10 that popular conservatism was once again to thwart reckless change. Last week, however, it is reckless change that had the momentum. This matters because, even if the “No” campaign rallies and pulls off a last-minute victory, the status quo has already been defeated. The issue of independence will not go away: The SNP will quickly persuade itself that only one more heave is needed to snap the rusty buckle.

In Westminster, there will be a battle to define what the “No” vote means and what it mandates. The phrase “devo-max” is now tossed around idly as if its significance is obvious but the extent of devolution to Scotland that will be politically necessary in the event of a “No” vote is unclear. The decentralisation of taxation and federalisation of the UK may well be the answer but the intellectual, political and cultural heavy-lifting required to make that happen has barely begun.

In the event of a “No” vote, Miliband aims to show that the changes required to answer Scotland’s cry of anger are economic and social as well as constitutional. Cameron’s challenge will be to maintain the degree of engagement he has mustered so far before delegating the whole wretched business to someone else. This, as much as Britain’s place in Europe and the challenge of the Islamic State of Iraq and the Levant (Isil), is a matter for the prime minister himself to oversee — however Scotland votes. The death last week of Dr Ian Paisley was more than a moment of great sadness for his family, those he represented and those with whom he worked.

It also showed how woefully short of heroes this referendum has been. Nobody could wish upon Scotland the horrors of paramilitary conflict and sectarian violence. That, emphatically, is not my point. What I mean is that Dr Paisley cared so much about the survival of the Union that he was willing to risk everything, to work with and eventually to befriend the political representatives of the IRA so that Ulster could be a peaceful part of the United Kingdom. His legacy is towering.

Meanwhile, across the Irish Sea, Scotland dithers over its destiny, caught in a fugue state of anger, resentment and indecision. It is as though the sheer scale of the question — the enormity of what is at stake — has not sunk in. History has crept up on the Scots, demanding a one-word answer. All we can predict with certainty is that nothing will be the same again.

— The Telegraph Group Limited, London 2014