If Boris Johnson is victorious, it will be the fault of an opposition in disarray

Is this a Brexit election? Well, yes and no. Escape the echo chambers of what Dominic Cummings, the Prime Minister’s chief adviser, calls “SW1” and you discover that the electorate is fretting about much more than the UK’s departure from the European Union.

This is not a single-issue contest, and it would be bizarre if it were so. At the same time, what we confront on December 12 is inescapably the defining electoral moment in the long and inglorious saga of political turmoil that was launched by the referendum of 2016.

If Boris Johnson secures a parliamentary majority, the deal he secured in Brussels will be passed by the Commons, possibly before Christmas. Any other result leaves the fate of Brexit in play, especially because the Democratic Unionist Party, that propped up Theresa May after 2017, is now Johnson’s implacable enemy, furious that Northern Ireland has been sold out to expedite the new withdrawal agreement.

I still find it hard to imagine Jeremy Corbyn, the Lib Dems’ Jo Swinson, and the SNP’s leader at Westminster, Ian Blackford, brokering any sort of arrangement — choosing a restaurant, for instance — let alone the basis of an anti-Conservative parliamentary deal that stops short of full-blown coalition (impossible) but is stable enough to turf Johnson out of Number 10.

However, with a real effort of will, it is just about conceivable. And, if it is conceivable, that means there could yet be a fresh referendum on Brexit.

All of which is to say that, while much else is at stake on polling day, this really is the fork in the road for those, on both sides of the argument, who have been arguing over Britain’s future relationship with the EU since January 2013, when David Cameron announced his intention to hold an in-out referendum. If Johnson wins outright, game over. If not, then not.

And it is this that the Leavers of all stripes understand with a ruthless clarity. As Anne McElvoy argued yesterday , Nigel Farage’s decision to withdraw Brexit Party candidates from seats won by the Tories in 2017 by no means seals the deal for Johnson. The Tories’ audacious core strategy depends, to the point of recklessness, upon the capture of Labour Leave constituencies in the Midlands and the North.

Farage has conspicuously declined to retreat from these heartlands. Yet it is striking that he is being urged to do so by Arron Banks, the tycoon who bankrolled Ukip when it was led by Farage, and was one of his fellow self-styled “Bad Boys of Brexit”. As Banks sees it: “The only way Brexit is going to get delivered is by a Boris majority.”

This is certainly the view of Donald Trump and those of his allies with whom Farage is in contact. Though I think he will resist a total climbdown before the deadline for candidate nomination tomorrow, the fact that he is under such pressure is eloquent in itself. The scent of victory fills Leavers’ nostrils and they are responding with corresponding focus.

Compare and contrast the woefully disaggregated performance on the other side. Yes, there is Unite to Remain, the tactical voting alliance between the Lib Dems, Plaid Cymru and Greens in 60 seats.

And there are individuals of integrity such as Tim Walker, who has stepped down as Lib Dem candidate in Canterbury to give the Labour incumbent, Rosie Duffield, a better chance of defending her seat. He is doing so, not because he wants to see Corbyn in Number 10, but because he wants a pro-Remain candidate to represent the constituency.

Yet that’s about it. In most places, there is little sense of the urgency of the hour — the absolutely pressing need (if you care about such things) to prevent Johnson from winning the additional seats he needs to end our 46-year-long relationship with the EU.

Partly, this reflects the unbelievable mess that is Labour’s Brexit policy. Corbyn would have us believe that he would negotiate a new deal, get it passed by a special Labour conference (always handy in these situations) and then put it to a confirmatory vote.

His timetable of six months is absurdly optimistic; much worse is the lack of conviction reflected in the whole plan. What does Corbyn really want to happen? Is Labour, as the shadow foreign secretary Emily Thornberry and departing deputy leader Tom Watson say, a Remain party, or not? At such a moment, the arrogance of Corbyn’s ambiguity on the most pressing question facing the nation he aspires to lead is breathtaking.

The corollary is detachment, defeatism and disarray in the political centre. Witness the retirement en bloc of scores of reliably sane MPs from all parties, sick of populism, polarisation and bullying: the asylum really has been handed over to the inmates.

Witness, too, as a hideous parable, the unforgivable mess at the People’s Vote organisation, wrecked by egos and allegations of sexual misconduct — a campaign given real energy and purpose by a cohort of young activists, but now torn to pieces by the narcissism of the middle-aged.

There is a long campaign ahead, and there will be many twists and turns. But if Johnson wins in 29 days’ time, posterity will not be kind to those of his opponents who failed to recognise quite how much was at stake, buried their heads in the sand, and waited for others to shape history.