Ever since Jeremy Corbyn’s election, his opponents had hoped, and his supporters had feared, that he would be forced to reseek nominations if challenged for the leadership. Having won the backing of just 15 MPs in 2015, he would always struggle to achieve 51 MP/MEP signatures.

Legal advice to Labour’s HQ stated that he was required to do so, while a separate assessment for the leader’s office suggested the reverse. But it was always politics (in the form of Labour’s National Executive Committee), rather than the law, that would determine the outcome.

In advance of yesterday’s six-and-a-half-hour NEC meeting, speculation grew that Corbyn would lose the vote. But in line with my exclusive report on Monday, he prevailed by a comfortable margin: 18-14. There was “no doubt,” a senior Labour figure had told me, that Corbyn would win even were a secret ballot used - and so it proved. As sources also predicted, the leader won the unanimous support of the 12 trade union delegates.

After his automatic inclusion on the ballot, the rebels were dismayed by the prospect of facing the landslider of 2015. But their despair soon 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 130,000 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 ithe 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 that on whether to charge £25 was won by 15-12.

The rebels believe that a shrunken selectorate works in their favour. They note that only a minority of members - 49.6 per cent - voted for Corbyn in 2015, compared to 83.8 per cent of registered supporters. A recent YouGov poll found that the leader’s approval rating among members had fallen from +45 in May to +3 and that 54 per cent wanted him to resign before the next general election. To counter any side in support, Corbyn’s allies hoped to again recruit tens of thousands of registered supporters. The two-day sign-up period is designed to curtail this possibility (as well as reducing the administrative burden on Labour HQ, which last time struggled to vet newcomers).

But some rebels fear a crucial loophole remains. “You can join Unite now and get a vote,” a Labour source swiftly noted. Affiliated trade union and socialist society members, 57.6 per cent of whom voted for Corbyn in 2015, will be permitted to register until 8 August. “Want a voice in leadership election?? Join a union and sign up as an affiliated supporter!” tweeted Unite’s Jennie Formby, an NEC member. The unwaged are able to join the union’s Community scheme for just 50p a week. New Corbynite members enraged at being denied the automatic right to vote, will be encouraged to join through social media. Some rebels fear the allegation of “gerrymandering” will only galvanise the left and deny them any chance of a fair hearing.

Many anti-Corbynites had long argued that they would only win by emulating their opponent’s example and reshaping Labour’s selectorate. They spoke of recruiting hundreds of thousands of centrist voters who craved a “proper opposition” and of harnessing “the 48 per cent” who voted for EU membership.

As I revealed in my column last week, an unpublished poll by GQR found that 10 per cent of the public would participate in a leadership election for £3. After being comprehensively out-organised by the left in 2015, Corbyn’s opponents founded the “Saving Labour” website to recruit new supporters. But the 48-hour registration period and £25 fee dramatically reduces the potential intake. “Amazing rebels think this a win,” tweeted Ed Miliband’s former pollster James Morris. “Centrists could’ve recruited millions if tried. Hollande had no charisma & got 1.8m.” Rather than moderate floating voters, it is the most ideologically committed, the most left-wing, who may be most likely to stump up £25.

Though Corbyn’s approval rating has plummeted, the same YouGov poll still showed him beating leadership challenger Angela Eagle by 50-40. Based on this measure, his support among members is in fact unchanged from 2015. Most of those who have joined since last September are, unsurprisingly, sympathetic to Corbyn. Faced with this deficit, the rebels long vowed to recruit, recruit and recruit again. The risk is that they have now left a door open for their opponents (through left-wing trade unions), while closing one for their supporters.

The adoption of Labour’s current electoral system in 2014 had the unintended consequence of enabling Corbyn’s election. As his opponents face a more left-wing membership than in 2015, history may be about to repeat itself.