On 24 September, at a special conference in Liverpool, Jeremy Corybn will be re-elected as the leader of the Labour Party. This, at least, is the outcome that MPs anticipate. The party’s leadership contest has more than five weeks to run but few believe Corbyn’s soft-left challenger, Owen Smith, will prevail. “Corbyn’s going to win and he could win at least as well as he did last time,” a former shadow cabinet minister said. Among constituency parties around Britain, the Labour leader won 285 nominations (nearly twice as many as he did in 2015). Smith had 53.

One recent afternoon in Milton Keynes, some of those helping to ensure Corbyn’s victory gathered to hear him speak. From the top of a fire engine, the Labour leader addressed a crowd of 1,500 outside the town’s railway station. The truck, provided by the Fire Brigades Union, is a permanent presence at Corbyn’s rallies. “All over the country, we’re getting a big turnout of people,” he told the crowd. “Some are party members [Labour is now the largest political organisation in western Europe]. Some are party supporters. Some come because they’re interested in politics for the first time, because they recognise that since a year ago, we are no longer the me-tooism of politics . . . A year ago, I’m sad to say that in parliament, the official Labour position was to abstain on the Welfare Reform Bill and the £12bn that was going to take from the poorest and most vulnerable in our society. No more is that the position. We want to defend and support those who are the most vulnerable in our society.”

Corbyn, jacketless and wearing a blue shirt, spoke for 35 minutes without notes. His audience listened raptly, frequently interrupting his rhetorical fusillades with cheers. “People were embarrassed to say they’re socialists before. They’re not now,” Gail Gallagher, a social worker, told me. The last Labour leader, Ed Miliband, “wasn’t up to it”, she said. “Too lightweight,” her husband, Neil, added.

Similar sentiments were expressed by John McGeechan, a 22-year-old postgraduate student who joined Labour after “self-indulgent, self-serving MPs initiated their corridor coup”. Of Owen Smith, who is running on a platform to the left of Miliband’s, he said: “He’s just another mealy-mouthed careerist who says whatever he thinks is going to get him elected. I don’t believe at all that he means what he says about creating a radical socialist government given that he’s got the backing of Peter Mandelson, Alastair Campbell and Tony Blair, people who’ve disagreed with Corbyn on pretty much all his socialist policies. I don’t believe that he’s going to stand up to these people.”

Some of those present were hardened activists, distributing revolutionary news-sheets for the likes of Labour Party Marxists and Counterfire. But many were relative newcomers to Labour, inspired to join by Corbyn’s unashamed moralism.

When the leader told the crowd that he wouldn’t read out all ten of his campaign pledges because “you don’t want to be here ’til sunset” some cried out, “We do!” (This prompted derisive social media comparisons with the followers in Monty Python’s Life of Brian: “Speak to us, Master! Speak to us!”) Corbyn later proudly tweeted that the rally was “the largest ever political meeting in the town’s history”, 49 years on from its foundation.

The host constituency (Milton Keynes North) is held by the Conservatives with a majority of 9,753 votes. In his stump speech, Corbyn alluded to this. “This leadership campaign is about leadership of the party, yes, but it’s also about our campaigning abilities, to offer people something different, something alternative – a society that cares for all, not nourishes the wealth of a few. That’s why we’re going to gain seats here in Milton Keynes at the general election.” To win power, he emphasised in his closing words, “you have to offer something very, very different”.

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Labour MPs agree that Corbyn is doing that. But the consequence, they fear, is electoral apocalypse. Corbyn’s personal poll ratings are the lowest of any opposition leader in history. “If Jeremy Corbyn wins [the leadership election], I think we face meltdown,” the Ilford South MP, Mike Gapes, told me. “I can’t see any circumstances in which he can win a general election. We could go down to 150 MPs or even less [Labour has 230]. That’s without the boundary changes. If there isn’t an early general election and Corbyn is still there in 2020, we’ll get wiped out.”

At a meeting of Corbyn’s own constituency party, Islington North, on 10 August, his former policy director Neale Coleman, who is now supporting Owen Smith, warned that “with Jeremy as leader, we would be ­defeated to the same level as in 1931” – when the party won just 52 seats.

It was such dystopian visions, and anguish over the EU referendum defeat, that led 172 Labour MPs to support a no confidence motion in Corbyn and 65 shadow ministers to resign. Few believe that the schism in Labour can be repaired. If Corbyn is re-elected, most MPs will continue to refuse to serve on the front bench, leaving him incapable of forming a full team. “We’ve crossed the Rubicon: there’s no going back,” Wes Streeting, one of the 2015 intake, told me. “This is irreparable while Jeremy remains leader.”

Such judgements lead some commentators to argue that a split is both inevitable and desirable. Conditions now, they say, are far worse than those faced by Labour MPs in the 1980s (when 28 joined the breakaway Social Democratic Party). The left today controls the leadership and not just the constituencies; it retains the support of most of the trade unions; a “one member, one vote” system has replaced the electoral college, to which the deputy leader, Tom Watson, wishes to return. Rather than persist with the unhappiest marriage in politics, Labour MPs and left activists – so the argument runs – should go their separate ways.

Advocates of a new centre-left party cite an increasingly promiscuous electorate, the Brexit-opposed “48 per cent” and a pool of willing donors. But it is not an option that Corbyn’s opponents intend to pursue. Labour's tribalists have no intention of leaving their party. The more tactically minded see little potential for a new grouping to flourish. A crowded electoral marketplace, the resilience of the Labour brand, the rebels' own divisions and Theresa May's economic interventionism all limit the space to occupy.

Others fear a lack of “big beasts” to lead a breakaway. “It would need a very strong, credible leader to lead people through such an incredibly radical moment,” Peter Kyle, the MP for Hove and Portslade, said. “The SDP had Roy Jenkins, it had Shirley Williams: very big, towering political figures with intellect and experience in government. That’s the kind of thing that you’d be looking for if you were going to take one of the radical options.”

He added: “There’s a lot of talk about whether the party will split. What it feels like to me is that the party has already split. It’s like one of those chasms you see in the Arctic. It starts very small at the top, a dusting of snow covers it; but underneath is this enormous gap, and when somebody steps on it you fall through. The little dusting of snow at the top, which is holding it together, is Tom Watson and Iain McNicol [Labour’s general secretary]. But underneath them is this yawning gap that any time could rupture. I think that has already happened. The question is whether we can put it back together again, or whether it will just snap.”

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If Corbyn is re-elected, another struggle for supremacy will begin. His allies want to replace both Watson, who was elected deputy leader last year, and McNicol, who has been general secretary since 2011. The former, who is from the party’s old right, outraged Corbynites when on 9 August he warned of “Trotsky entryists” who were “twisting young arms”. “I voted for Tom Watson!” Gail Gallagher said angrily, in Milton Keynes. “What a snake.”

Corbyn’s allies accuse McNicol of aiding the attempt by members of the National Executive Committee to prevent his automatic inclusion on the ballot and of tacitly supporting Smith’s campaign. The leader’s team alleges that Smith had early access to members’ email addresses and was given advance sight of the questions for the first hustings in Cardiff on 4 August. They are further aggrieved by McNicol’s successful court appeal against the inclusion in the contest of 130,000 people registered as Labour members since January.

After much discussion of the party’s “woman problem” following Angela Eagle’s failed leadership bid and the selection of an all-male roster of mayoral candidates, allies of Corbyn joke that replacing McNicol with a woman would “kill two birds with one stone”. Jennie Formby, an NEC member and former political director of the Unite mega-union (who has a child with Len McCluskey, Unite’s general secretary), is touted as a possible successor (Unite sources emphasise that she is not interested in the post).

Control of the party bureaucracy is regarded as essential to completion of Corbyn’s internal revolution. The leader’s office has long believed that Labour staffers are working to rule, at best, and plotting sedition at worst. But Corbyn’s opponents say that he lacks the support required to remove the general secretary. The GMB union, which endorsed Smith and of which McNicol is a former political officer, is among the reputed majority on the NEC for Owen Smith. But a Corbyn source warned: “McNicol has pissed off a lot of [trade union] general secretaries. The GMB alone won’t be enough to save him.”

As the party’s elected deputy leader, Watson cannot be removed without a challenge initiated by at least 50 MPs or MEPs – a threshold that cannot be achieved. But Corbyn’s allies float potential rule changes such as term limits or the introduction of an additional female deputy. In this way, Watson can be undermined. “If MPs like Jess Phillips and Caroline Flint want to propose that, the leadership will be behind them,” a source said.

The trade unions and Corbyn supporters in Momentum, the activist group launched after his leadership victory last year, are pushing for a remodelling closer to home. They speak of having “bailed out” the leader’s office after a succession of unforced errors over the past 11 months. The TSSA transport and travel union and the Communication Workers Union, which provide much of the campaign’s organisation and give it financial heft, are likely to demand additional personnel in Corbyn’s office. Sam Tarry, the TSSA’s national political officer, is tipped to make a full-time move to the leader’s spin operation to assist his communications director, Seumas Milne (the Guardian journalist whom even his opponents now regard as unsackable).

The overarching question remains how Corbyn operates with a parliamentary party that has declared no confidence in him. Watson has proposed the return of shadow cabinet elections, which were abolished by Ed Miliband in 2011. This would enable MPs to choose as many as 20 of their own number, to whom Corbyn would assign portfolios. “That would be one way for him of peacemaking,” a former shadow cabinet minister said. “If that were the case, I’d be prepared to put myself forward.”

However, a Corbyn source dismissed the idea. “It’s not going to happen,” he said: “they don’t have the numbers to get it through conference.” He added that the election of a representative for the Parliamentary Labour Party was a possibility.

He went on: “Jeremy is one of the most concessionary politicians around. He’d be very open to the idea of bringing people back, sitting down, listening to where things went wrong and where the input would be from the other side – seeing where there can be mutual ground.”

Corbyn’s team does not hesitate to warn that antagonistic MPs are putting themselves at risk of deselection by members. “The power’s there, we can’t stop it. We cannot say, ‘You cannot use the powers at your local CLP [Constituency Labour Party],’” a source said. “There’s no lever in the leader’s office for deselections. The issue is that there’s lot of party members who are very annoyed at their MPs for going against them, and now they find they have a voice that they never normally had.”

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In Milton Keynes, the student activist John McGeechan rebuked Owen Smith for comparing Corbyn to an ­employer who tells staff to “work harder or I’m going to sack you all”. What the challenger didn’t understand, he said, “is that Corbyn’s not their employer: we are”. The debate that defined Labour’s struggles in the 1980s – whether MPs or activists should hold the whip hand – has been resurrected.

Although mandatory reselection was abolished by Neil Kinnock in 1990, MPs can be ousted if they lose the “trigger ballots” held automatically before a general election (from which open selections result). During a recent visit to Brighton, Corbyn said that he would not “interfere” in attempts to remove the local MP Peter Kyle. “What goes on in CLPs is part of a democratic process,” he stated.

“I think a lot of other people were shocked. I wasn’t shocked or surprised,” Kyle said. “What Jeremy does is, he stands passively by while bad things happen. When Ruth Smeeth [a Labour MP] was attacked at the launch of the anti-Semitism report [by Shami Chakrabarti] he sat quietly by and didn’t even open his mouth.”

Kyle added: “When Diane Abbott attacked Jo Cox for writing an article with [the former Conservative cabinet minister] Andrew Mitchell about international development, Jeremy Corbyn did not say a single word when he was asked at the PLP meeting whether his front bench should be attacking new-intake MPs. He didn’t even speak . . .

“Part of the responsibility of a leader is to proactively stop bad things from happening. For me, what Jeremy said when he was down in Brighton is part of the pattern I’ve seen from the start.”

MPs warn that a wave of deselections could lead to the formation of a breakaway parliamentary faction, as long advocated by the former Harold Wilson aide Joe Haines. "If people have got no seat and they know they're not going to be in the next parliament they've got nothing to lose," one said. Frank Field told me last year that any MP deselected should trigger an immediate by-election and stand as an “independent Labour” candidate.

Corbyn allies hope to achieve rule changes such as mandatory reselection and a reduced leadership nomination threshold (from 15 per cent of MPs/MEPs to 5 per cent) by 2017-18. The “full democratisation” of the party, as they describe it, would guarantee the presence of left-wing candidates in future contests. Corbynism would endure even if Jeremy Corbyn did not.

In private, Labour MPs are increasingly critical of Owen Smith’s campaign. The former shadow work and pensions secretary, who entered parliament in 2010, was chosen as a “clean skin”, untainted by the Blair years and the Iraq War. But the Welshman, who has worked as a lobbyist for Pfizer, has struggled to reconcile his past positions, such as support for private-sector involvement in the National Health Service, with his left-wing, Corbyn-style policy platform: railway renationalisation, a ban on zero-hour contracts, a full “living wage” and a wealth tax on the top 1 per cent of earners.

“The view was that you needed to do a soft-left candidacy to see if that would work,” a former shadow cabinet minister said. “But Smith’s message appears to be: ‘I’m the same as him but I’m more competent ; I look better in a suit.’ Or it’s a warmed-up Ed Milibandism, which was rejected by the voters.”

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In a Morning Star article in 2003, Corbyn suggested that there should be “an annual election for leader”. His wish may now be granted as his opponents mount repeated challenges to his leadership.

“Moderates need to understand that it’s only through the registered supporters route that they’re going to be able to win back the party,” a former shadow cabinet minister said. “There are lots of people out there who want a credible, electable, centre-left proposition and we have not given them enough of a reason to sign up . . . The strategic problem with Owen’s candidacy is that it talks to the existing bubble. You can win 40-45 per cent with that, but you can only really win if you can bring in new people. Who has an offer and the charisma to be able to bring in new people? That has to be the question the next time round.”

Some point to the primaries in which the French president, François Hollande (backed by 1.6 million supporters), and the Italian prime minister, Matteo Renzi (1.9 million), won against more left-wing opponents as models to emulate. Another mentioned the United States: “Obama would never have won in 2008 with the existing Democratic membership and support base – it was owned by the Clintons. You’ve got to change it.”

Rebels say that another leadership challenge could be triggered early next year, in advance of a potential general election. But others believe that they should follow Thumper’s law: “If you can’t say something nice, don’t say anything at all.”

A senior MP argued that the PLP should “just shut up” and “let Jeremy crack on with it”. The imperative, he said, was to avoid MPs “taking the blame for us getting thumped in a snap election”.

Corbyn, some MPs fear, could even survive defeat in an early general election. “Don’t make the mistake of thinking that Jeremy will go easily,” Kyle said. “These people do not believe Jeremy is capable of making any mistake and the people we’re talking about here, in the last thirty to forty years, have never admitted to any mistake of any kind. If we lose a general election that the Jeremy Corbyn Facts website [set up by Corbyn’s team] has already written the script for what would come. They would blame it on the 172 [MPs]. They would blame it on the conspiratorial coup attempt . . .”

Both sides in Labour’s struggle cite history in their favour. Corbyn’s opponents highlight his record of rebellion against every leader since 1983. His supporters assert that it was New Labour and its legacy that led to the election defeats of 2010 and 2015. Both are now torn between those who advocate confrontation – further leadership challenges and deselections – and those who plead for co-operation.

“All MPs are going to have to accept that no one has a monopoly on grievance,” Clive Lewis, the shadow defence secretary and a Corbyn ally, told me. For his own constituents in Norwich, Lewis said, Labour’s imbroglio was like “a Dallas plot on speed”.

“They can’t keep up and they’ve lost interest,” he said. “It’s not even about electability: it’s about simply being relevant. We’re becoming an irrelevancy to people; we’re becoming a joke.”

There is one point on which Jeremy Corbyn and his most recalcitrant opponents converge: voters do not like divided parties. The risk for both – and, indeed, the future of the Labour Party – is that they will soon discover just how much.