Protestors on the anti-Brexit marches have sensed an eerie absence. ‘What is it?’ I thought back in March as I stood on a soapbox to address an audience so jammed by the weight of numbers on Park Lane that it could not escape. Then it hit me. ‘What the hell have they done with the left?’

There were no Socialist Workers Party placards or George Galloways. The people who hijacked every demonstration I could remember had vanished. I saw plenty of left-wingers. On the neighbouring soapbox, a succession of socialists spoke well on the need to protect migrants and workers’ rights in a reformed Europe. But they were leftists, not the left: the left of Jeremy Corbyn, Seumas Milne, Len McCluskey, the Communist Party of Britain and Stop the War; the left that thinks historians give Stalin a bum rap; the left that will excuse Saddam Hussein, Slobodan Milosevic, Nicolas Maduro, Iran, Russia, Hamas and Hezbollah; the anti-European and anti-Semitic left; the bully left; the crank left; the left that no amount of shame could kill. Until now.

What was obvious in London is obvious everywhere. Brexit can destroy the left — and Labour with it. Like vultures, the Liberal Democrats, Greens, Change UK and the Scottish and Welsh nationalists are already swooping down to feast on, well, the remains. The Lib Dems, written off by the left as Tory collaborators, are enjoying the heartiest meal. A poll for last weekend’s Observer found that, within the space of four weeks, they had roared ahead of Labour to become the favoured party of Remain voters. To date, 37 per cent of Labour’s 2017 general election vote had defected to the Lib Dems and Greens. I don’t believe the defections are over yet.

The malicious among you should savour the moment. For the first time, Labour is controlled by men who denounce the Labour tradition as a sellout. They announced themselves as the true radicals who would revolutionise party and country. Now, in a pattern found in all revolutions, yesterday’s radicals are today’s conservatives, unable to control or comprehend the fury around them.

Propagandists tell us Labour has no choice but to avoid hard choices. Realpolitik demands it ducks the great issue of the day. Never mind that the far left once denounced realpolitik and said, in Karl Marx’s words, that the point was to change the world, not accommodate oneself to it.

Consider instead the folly of the notion that Labour cannot commit to campaigning to remain in the EU. I concede that doubletalk worked for a while. In the 2017 general election, millions fell for it. But as the saying goes, ‘Fool me once, shame on you. Fool me twice, shame on me.’

Corbyn has taken a senseless political risk by treating his voters as fools. The British Election Study estimated that two thirds of Labour voters went with Remain in the 2016 referendum. Now YouGov estimates that 88 per cent back Remain. Any party that goes with the 12 per cent rather than the 88 per cent will collapse. It is not a party for the many, but for the few.

The far left has been so busy fighting the hated ‘centrists’ that it has forgotten to fight the right and far right. Existing and former Labour supporters have not been so negligent. They need only look at the tribunes of Brexit — at Gerard Batten, Nigel Farage, Boris Johnson, Jacob Rees-Mogg and Dominic Raab — to know that they must be opposed. There is an almost primitive fear at work. If a film company had searched for characters guaranteed to set the tom-toms of liberal England beating out a warning, it could not have found better candidates than these gentlemen.

The Labour leadership says it must support Brexit, and offer messages on a second referendum so half-hearted that no one believes them, to retain Leave seats in the north. Yet in a first-past-the-post general election, with the vote split three, four, even five ways, there’s no such thing as a Leave or Remain seat. The party that collects a plurality of the vote wins, and if Labour drives away northern Remain voters then it will lose.

Labour is maintaining that it must woo people who don’t vote for it, and ignore those who do. At any period of electoral history this would be a risky proposition. But when voters have never been more mobile, it shows how dated the debased Stalinist culture that so many of Labour’s key figures spent their lives imbibing has become. The central committee is supreme. Lowly comrades have no choice but to obey. Their command-and-control tactics are bound to fail, but that is not the worst of it.

Mary Creagh, Anna Turley, Bridget Phillipson, Phil Wilson and many more Labour MPs in supposedly Leave-dominated northern constituencies are supporting a second referendum, not only because it makes electoral sense, but to protect their constituents. Any kind of Brexit will hit the poorest regions of Britain hardest, while a no-deal Brexit would be catastrophic (I hear readers dis-agreeing, but I am trying to tell you how my side thinks, not how you think.)

A Labour leadership that pretends all will be well if we get a cuddly Labour Brexit rather than a wicked Tory Brexit has succeeded only in provoking a revolt. ‘I will not tell my constituents that leaving the EU will make them more prosperous, more equal or more free,’ said Bridget Phillipson. Conventional media wisdom holds that she will now lose her Sunderland South seat. But conventional media wisdom has been so wrong, so often, I’m surprised it dare show its face in public. In her protest, incidentally, lies the answer to Corbyn and his supporters who yearn for the day when they can stop talking about Brexit and concentrate on the ‘real issues’. We’d all like to do that. If Britain leaves the single market, however, centre-left measures will be immeasurably harder to implement, which is why I suspect so many on the right are so keen to do it.

‘The single biggest dysfunction in Britain now is the disconnect between the leaders of the Labour party and Labour supporters,’ a senior figure in the anti-Brexit campaign told me. They have had enough of Corbyn telling them that a vote for Labour in 2017 was a vote for Leave and, more brazenly, that the success of the Greens and Lib Dems in this month’s local elections proved the public wanted to ‘get a deal done’.

As they abandon the party in their millions, realisation is dawning on Labour politicians with an eye on the leadership that they may have made a career-threatening error. ‘You don’t need a weatherman to know which way the wind blows,’ sung Bob Dylan. He was right. In the Labour party, all you need is Emily Thornberry — and she has now come out for a second referendum.

Can Corbyn save himself by doing the same? The essential fact, too easily forgotten, is that the Labour leader and his entourage come from an odd fragment of the post-communist left. It opposed the European project as thoroughly as Farage and Johnson have done: the sole difference being that Labour’s militants believe Britain can cut itself off from Europe and build state socialism in one country while their mirror images on the right prefer small-state capitalism. Mutatis mutandis, they agree on the fundamentals.

Corbyn is impressed by the 20 per cent of his Islington North constituents who signed a petition calling for the revocation of Article 50. (‘Signing petitions is something Jeremy understands,’ sighed one Labour source.) Suppose in the coming days that Corbyn capitulates to electoral reality and comes out for a second vote.

Labour’s position is not as dire as it seems. In Scotland, it is finished for the foreseeable future, and in Wales there are signs that Plaid Cymru could replace it as the anti-Tory alternative. But in England, Change UK has made a monstrous mess of creating a new party. The Greens are growing in strength but are still on the fringe, while the Liberal Democrats lack political talent and remain a rural and suburban party unable to challenge in the Labour cities.

Labour Remainers are adamant that a formal shift in policy would not be enough. Just as May had to sack Nick Timothy and Fiona Hill after their disastrous advice led to the loss of the Tory majority in 2017, no change in Corbyn’s position would be credible if his advisers remained in place. Andrew Murray, from the Communist Party of Britain, Seumas Milne, a fellow traveller, and Unite’s Karie Murphy and Len McCluskey are the ‘brains’ behind Corbyn’s opposition to the EU. They would need to be shut out of decision-making or shown the door.

I can’t see Corbyn doing that. Even if he did, the inability of professed revolutionaries to understand the dynamics of a revolutionary crisis could still do for him. It is worth remembering that the People’s Vote campaign was formed only in April last year. If May and the wider right had not talked as if half the country were treacherous citizens of nowhere, and if supporters of Brexit had been able to agree on a common position, we would be out of the EU. But the same radicalisation that pushed the hardcore of Brexit supporters into ever more extreme positions has produced an equal and opposite reaction among their opponents. No senior politician or campaign group supported the Revoke Article 50 petition, for instance. But six million people signed it in March.

The organisations around the People’s Vote campaign are on the move, too. They are not content with demanding a second referendum. They want politicians to start telling the public a truth that’s overdue a hearing: Britain’s problems are made in Westminster, not Brussels. We can’t face them because of Brexit, and the only way to face them is to stop Brexit.

Their strategists, meanwhile, are thinking ahead. The Tories, they assume, will elect Johnson or someone like him, who can cut a deal with Farage or so mimic his policies that there is no point in voting for his Brexit party. Johnson, or a Johnson clone, will not get more concessions from the EU and won’t get a no-deal Brexit through parliament. They will have to back down or call an election. As I said, the party with the plurality of the vote (however small) wins the seats. The only way to stop a united Brexit right beating a divided Remainer centre-left is for the opposition parties to agree an electoral pact. This would be hard enough to arrange in the best of times. No one believes a sectarian far left that can’t ally with critics in its own party will step aside for the Liberal Democrats and Greens. Continuing failure will reveal the Corbynistas’ inability to cope with the demands of a Britain in crisis. As their failure becomes more evident, the revolt against Labour will grow.

Revolutions devour their children. How strange but fitting it is that the Brexit revolution should pick the far left for its starter.