The vote of no confidence in Dominic Grieve shows the Tories are, like Labour, vulnerable to bolshiness in their own local associations. In fact, the Conservatives might turn out to be more effective at purging MPs because, for all of the noise, the Corbynites have not done much. And if Jeremy Corbyn ends up in No10 after a snap general election, he may soon wish that he had done more.

Two polls in the past 24 hours have been pretty good for Labour. Opinium has them level-pegging with the Tories on 35 per cent while Delta gives them a five-point lead (though this falls to three points when respondents are given the option of Change UK). On these polls, Labour would form the largest party in the Commons - but it would not have a majority. In which case, Corbyn could expected to be hemmed in by his rebels to a far greater extent than Theresa May is being constrained by the ERG.

The Corbyn project has three stages: 1) Change the Labour Party. 2) Form a government, preferably a majority Labour one. 3) Change the country for generations to come in the way Attlee and Thatcher did. The first stage has been completed in record time. It took a decade to transform Labour from a Clause Four socialist party into a metropolitan centre-left one but the Corbynistas have embedded progressive populism in a third of the time. The leadership, institutions, membership and activist base are solidly committed to Corbyn and Corbynism, even if the latter is still poorly defined.

The second stage, winning power, won’t be as easy. If we are on the brink of a trend back to Labour in the opinion polls, Corbyn might end up leading the largest single party (and might soon be odds-on to do so). Labour could then govern as a minority administration, perhaps with supply and confidence from the Scottish Nationalists. In this scenario, the SNP would operate in much the same way that the DUP has in its pact with the Tories.

Nicola Sturgeon would demand a princely ransom for her votes: including, I would expect, a cash handover higher than the DUP’s £1bn and devolution of referendum powers to the Scottish Parliament. The latter would, in effect, be agreeing to a second referendum on Scottish independence, which would be unpopular with most Labour voters north of the border and risk an even greater constitutional upheaval on the heels of Brexit. Corbynistas will take anything that gets their man into power but being propped up by the SNP, if it leads to the dismantling of the UK shortly thereafter, would drop a Brexit-style atom bomb smack-bang in the middle of a Corbyn government’s legislative agenda.

The last stage - an overhaul of British society - is a big ask for any government. But it would be uniquely trying for a Corbyn ministry, especially if he still had a minority government. Every prime minister has a backbench awkward squad that makes their life difficult. Attlee had the Left, Maggie had the wets, Blair had the anti-war bolshies. But these were factions of a single party.

The Labour MPs who oppose Corbyn already constitute, in effect, a party within a party (let’s call it Anti-Corbyn Labour) and look to their unofficial leader Tom Watson rather than Jeremy Corbyn. If it was to govern effectively, or at all, a Corbyn frontbench would have to manage two parliamentary parties — the PLP and the ACPLP.

This places a handbrake on any radical policy a Corbyn-run Number 10 might wish to pursue. On the economy, Corbynistas and anti-Corbynistas are much closer than either wishes to admit but on foreign policy, defence, immigration, welfare and public ownership there are significant differences. If these MPs are happy to work openly against him when he’s Leader of the Opposition, why wouldn’t they do the same if he becomes Prime Minister? The stakes would be so much higher at that point, when Anti-Corbyn Labour would find itself in the position the ERG does today, able to hold its own government to ransom. The leadership might see these MPs as patsies, and on antisemitism they have been, but what happens if the patsies summon a collective backbone?

Government by the consent of Jess Phillips might be a reassuring prospect for moderate voters, who would want to see Corbyn on a tight leash, but it can hardly appeal to true believers. Confronting this problem would lead to conflict and division, which Labour can ill-afford with a Tory government that daily appears ready to implode, but keeping the peace comes with consequences. Just as the Tories cannot achieve full-throated Brexit with a sizeable contingent of Remainer MPs, the Corbyn project could find itself suddenly strangled upon entering government. As Lenin warned: ‘If compromise continues, the revolution is doomed.'