On the evening of 12 July, more than a fortnight after the rebellion against Jeremy Corbyn began, his opponents played their final card - and lost. A vote of no confidence by 81 per cent of Labour MPs and 65 frontbench resignations had failed to dislodge him. The rebels’ last hope of avoiding another leadership contest against Corbyn was forcing him to reseek nominations. After being backed by just 40 colleagues in the confidence vote, all sides knew that the leader would struggle to achieve 51 signatures from MPs and MEPs.

Legal advice provided to Labour had stated that the incumbent should not be automatically on the ballot. It was this view which was adumbrated by lawyer James Goudie when the National Executive Committee (NEC) assembled at the party’s Victoria Street headquarters on 12 July. Rebels had cited the precedent of 1988, when Neil Kinnock was challenged by Tony Benn and achieved the requisite nominations. "That’s the rules, and anyway, I’m not going to hide behind incumbency,” the then leader told his campaign manager Robin Cook.

As Kinnock recalled in a piece for the New Statesman on 12 July: “To us, it was vital that the leader of a party committed by constitution, history, and conviction to the parliamentary road to socialism was able to prove wide support among the elected Labour MPs as well as the broader movement.”

Regardless of legal opinion, many felt that Corbyn should defer to this view. But faced with the possibility of the leader failing to make the ballot, to the outrage of his supporters, Labour’s NEC backed him by 18-14. Throughout the day, speculation grew that Corbyn would lose the vote. At the start of the six and a half hour meeting, the NEC agreed by 17-15 to hold a secret ballot, regarded by some as an omen of defeat. But as I reported on 11 July, senior Labour figures believed Corbyn would prevail even in these circumstances. With the support of left-wing allies such as shadow business secretary Jon Trickett (who replaced leadership challenger Angela Eagle) and trade union delegates, the leader was automatically included on the ballot.

But the rebels' despair swiftly turned to hope. After Corbyn had left the meeting to greet supporters outside, the committee voted in favour of a six month freeze date for members. The hundreds of thousands who have joined the party since 12 January (most of whom are thought to support the leader) will not be automatically eligible to vote. By contrast, in 2015, members had until 12 August (a month before voting closed) to sign up. Registered supporters, the group among whom Corbyn performed best last time, will have just two days to do so (18-20 July) and will be charged £25, rather than £3. Those who have paid £47 for membership in the last six months will need to pay twice over to participate.

“It’s game on,” a senior Labour figure told me afterwards, deriding the “hubris” of Corbyn. Had the leader remained to vote, a Unite amendment proposing a freeze date of 24 June - the day after the EU referendum - would have passed. A vote on whether to extend the sign-up period to a week was lost by 16-10, while the rebels won that on whether to charge £25 by 15-12. "He [Corbyn] is absolutely fucking beatable," a Labour MP said.

But even if the rule changes favour the rebels (and they may not do), Corbyn begins his second leadership contest as the unambiguous favourite. His opponents' continuing failure to agree on a single "unity candidate", with both Eagle and Owen Smith competing for the title, reflects the absence of a pre-eminent alternative. Eagle, who deputised for Corbyn at Prime Minister’s Questions until her resignation, is admired by MPs for her work ethic, tenacity and intellect. After 116 years, and two female Conservative prime ministers, she would give Labour its first woman leader.

But her campaign launch on 11 July underwhelmed many in the party. Eagle struggled to offer a dividing line with Corbyn other than electability: the narrow turf on which his opponents lost in 2015. "One of the big reasons candidates like Tessa Jowell and Andy Burnham struggled last summer was that they put too much message emphasis on winning," Marcus Roberts of YouGov told me. "When you say 'winning' to the PLP [Parliamentary Labour Party] they think of landslides. But when you say 'winning' to today's membership they often think it implies some kind of moral compromise."

To beat Corbyn, Eagle needs to reach activists' hearts, rather than merely their heads. But in the view of some, she failed to even do the former. When asked why she could beat Theresa May, Eagle simply replied: “Because she’s a Tory” (seemingly disregarding the result of the last two general elections).

While a recent YouGov poll found that 54 per cent of members wanted Corbyn to resign before the general election (and to do so immediately in the case of 44 per cent), it also showed him beating Eagle by 50-40. The leader’s team believe they can exploit her past support for the Iraq and Syria military interventions. One aide described it as a "major strategic error" to appear alongside Hilary Benn, who last year dramatically challenged Corbyn over the latter.

It is partly Eagle's "Iraq/Syria problem" that explains the increasing support for Smith, who opposed both actions. The former shadow work and pensions secretary, who first revealed his leadership ambitions in an interview with the New Statesman in January, has won the backing of prominent soft left MPs including Lucy Powell, Heidi Alexander, Chris Bryant and Kate Green. But others fear that the Pontypridd MP's hitherto low profile will hinder his bid. They also charge him with excessive personal ambition. A former shadow cabinet minister spoke of being "taken aback" by the anger towards Smith in the tea rooms. "It's a bit too much about him and not enough about the party," one MP told me.

Corbyn's opponents maintain that he must ultimately face only one candidate. But when and how either Eagle or Smith will prevail remains uncertain. Whoever the challenger is, some rebels already privately predict that Corbyn will win again. It is this likelihood that conjures the spectre of a split. Advocates argue that an increasingly promiscuous electorate, a willing pool of donors and "the 48 per cent", who backed EU membership, create fertile space for a new party. Unlike in the 1980s, Labour's far-left controls the leadership (rather than merely influencing it) and enjoys the formal backing of the major trade unions (once bastions of the right). Corbyn's opponents, the argument runs, should stop fighting a losing battle and play a smarter game.

But though the possibility of a split fixates the media, it is one that few MPs genuninely contemplate. Senior figures of the kind any breakaway would depend on, believe that first-past-the-post remains an irrevocable barrier to success (as the SDP and Ukip testify). The enduring potency of the Labour brand and Theresa May's centrist positioning are further deterrents. Finally, it is tribalism, a characteristic more often found on the party's right than its left, that motivates their loyalty.

"The thing with splits is it almost gives the impression that there is a 50-50 divide," Stephen Kinnock MP told me. "But there so clearly isn’t. I think it would be better to call it a spin-off. About 10 per cent of our PLP [Parliamentary Labour Party] would be very welcome to go and form the Socialist Workers Party. That’s what they’ve always wanted to do, they’re entryists. What an entryist does is come in through the back door, squats inside the house for a while until he’s wrecked it and then leaves through the front. And that is exactly what they’re wanting to do here. They’ve very welcome to go off and form their own party. We are the Labour Party, we represent the mainstream 9.3 million people that voted Labour and the others are very welcome to go off and do their own thing."

Aware that they will likely lose to Corbyn, the rebels speak of reducing his mandate and of laying the ground for future success. "Whether or not Angela wins, the fact that we’re able to build infrastructure and acquire data on moderates strengthens our cause," an Eagle supporter told me. They believe that the sight of a non-functional opposition against a new government will progressively shift membership opinion in their favour. Should Corbyn still refuse to resign, a senior MP vowed to "fight, and fight, and fight again", echoing former leader Hugh Gaitskell’s words to the 1960 party conference. Watson, Dan Jarvis, Chuka Umunna and Yvette Cooper are spoken of as potential future challengers.

May's insistence that she will not hold an early general election could buy the rebels more time. But the most pessimistic fear that they will inevitably fail to remove Corbyn, leaving them to face a "wipeout" (in the words of Wes Streeting MP). They warn that Labour could endure its worst result since 1931, falling below 150 seats. It is the national electorate, rather than the party selectorate, some predict, that may ultimately defeat Corbyn. The question is whether what remains will have been worth fighting for.