Theresa May has cracked. And of all the elemental forces that did the cracking, Jeremy Corbyn deserves the greatest credit. With just nine days to go until a no-deal Brexit, May was forced to face down her own cabinet, take no deal off the table, and invite Corbyn – who she’s otherised and vilified as not fit to govern – into talks in which he has the whip hand.

Whatever the outcome of those talks, the power shift in the past 10 days is obvious: from the European Research Group to the liberal wing of the Tories, from the government to parliament, and from the Eurosceptic wing of the Parliamentary Labour Party (PLP) to the membership. It can always shift the other way, and we are still several moves away from checkmate, but we can still draw a provisional balance sheet on the way Corbyn has fought May’s Brexit plans.

First there was the phoney war: between the 2017 general election and the publication of May’s “Chequers plan” in July 2018, all Labour did was pledge to enact its own version of Brexit, outline its six tests, reassure European migrants that it had their back and wait.

Then came Chequers. After a spate of cabinet resignations, hurried rewrites and an open Tory split, the ultimate truth became clear: no form of Brexit available is acceptable to the Brexiteers. At that point I, and others on Labour’s left, realised there was no majority for Brexit in this parliament and that it would have to go to the country again.

At Labour’s 2018 conference, the Lexiteers among Corbyn’s shadow cabinet and the Unite union were defeated. The membership committed Corbyn to (a) pursuing Labour’s own positive solution – a customs union plus dynamic regulatory alignment with the single market (b) keeping all other options on the table including (c) a second referendum. The standing ovation for Keir Starmer disabused Corbyn’s advisers of the impression that the membership would accept anything short of that.

Then, in December, the Lexiteer fightback began. Five members of Corbyn’s shadow cabinet at one point said they would resign rather than vote for a second referendum; meanwhile numerous junior shadow ministers, among them prominent BAME politicians, said they would resign if Corbyn did not back another referendum.

Fast forward to late March and this potentially dangerous cleavage in the Labour left was largely healed. Why? First, because Corbyn reacted intelligently to the threat of a right-wing split from Labour. The Independent Group (TIG) is a hopelessly compromised dark money organisation that will disappear at the next general election. But when Tom Watson set up Future Britain – an unannounced faction of traditional centre-left politicians in Labour, who could theoretically destroy Corbyn’s position as leader of the opposition – the atmosphere changed.

Though the Labour whip for the full conference position was applied lightly at first, it became stronger as the weeks progressed. You still came across the odd deluded northern English backbencher who believes Seumas Milne is sending them coded messages via the pipework in the Norman Shaw Building, ordering them to defy the whip. But on the evidence of last week, the whip is being applied vigorously, with Corbyn himself taking an active role in persuading lifetime Eurosceptics to toe the line.

As a result, we know the answer to the question of which party disintegrates first – it is the Tory party. Yes, Chuka Umunna and co. have flounced out, but few people care. TIG has no members, no base in UK civil society and has even managed to alienate the blue-blooded liberal elite who finance the People’s Vote campaign. And yes, Watson’s group is powerful – and Watson himself has grown in stature as a politician.

But Labour has stuck together for a reason that the Tory party and its press pack can barely understand: for us this is not a career, it is a cause. And for us, the cause of peace, democracy and social justice is bigger than Brexit. We can lose strikes, jobs, dreams – and still bounce back the next day with our belief in a socialist future undimmed. Whatever the outcome of Brexit it will be secondary to our overall goal.

The Tories, by contrast, have split because hard Brexit became their goal, indeed their obsession. Corbyn, a vilified outsider, will walk into negotiations with the Prime Minister today on equal terms: not because of superior statecraft (though he and his advisers have shown some) but because the Labour movement is built on solidarity while the Tory party is based on selfish entitlement and greed.

What happens next will happen fast. There will be some inside the PLP who want to negotiate a soft Brexit deal without a second referendum. But it’s a non-starter. While the Polish trade union Solidarnosc once negotiated with the authorities with a microphone in the room, linked to a speaker to the crowd outside, Corbyn does not need to. Everything he says in the negotiation will be leaked to the right-wing tabloids by the May’s advisers. He has no option but to ask for Labour’s full Brexit proposal – as outlined in IPPR’s “shared market” report – and for a referendum to confirm it.

As a reminder of the position he’s mandated on, it does not just just call for a second referendum but outlines the following principle: “If the government is confident in negotiating a deal that working people, our economy and communities will benefit from they should not be afraid to put that deal to the public.”

And this is no longer just a Labour conference motion: it has become the Kyle-Wilson amendment around which current attempts to find a parliamentary compromise revolve. The principle is that Labour will only vote for any Brexit deal if it is put to a confirmatory referendum. And if, up to now, it’s been pro-Remain voters who want that vote, once Leave-voting public realise what has happened, they too will clamour for a final say.

If May had any tactical nous, the one concession she could make is a long extension to Article 50 during which there would be a general election. That would overcome the objection that “we can’t sign a deal if the next parliament, and next Tory leader, has the right to junk it”.

But the words May and tactical nous should never appear in the same sentence. She is cloth-eared to the public mood. Her podium speech blaming MPs for the impasse she created; and her silent, deflated turns away from the cameras in the deserted rooms where she makes her statements, are all evidence of a politician on borrowed time.

I’ve had my criticisms of Corbyn: he’s listened too much to Lexiteers with no political base in the party; he was slow to apply the whip to rebels; communication with party members have been excruciatingly bad, especially over the decision not to attend the People’s Vote march.

But, like one of those Russian field marshals in Tolstoy’s War and Peace, who wins by sitting on his horse and doing nothing, Corbyn’s generalship has, for now, caused the enemy to break and panic.

Once Tory ministers posed in the power stance. Soon they will find out what the no-power stance feels like.