By Chaminda Jayanetti

In the Labour party, you can be both the carcass and the vulture. While Jeremy Corbyn's Labour leadership suffers death by a thousand polls, the Corbynites themselves are looking to salvage what they can from what currently looks like an electoral apocalypse.

A leadership challenge is all but certain unless Labour pulls off an exceptional turnaround - and then the question becomes whether Corbyn will go.

For Corbyn to stay and fight his third leadership election would be a risky strategy for his backers. Fewer Labour members would be willing to blame Labour MPs for the party's strife after a chastening general election defeat than was the case last summer. If he faces off against a credible centrist candidate running a smart campaign, enough members might be persuaded to give up on the Corbyn project - especially if he faces a woman. If so, the Corbynites would lose everything.

The 15% problem

The Corbynites' dilemma is the widespread assumption that were he to quit after the general election, no left-winger would get on the ballot to replace him. When there is a vacancy at the top, leadership candidates need the support of 15% of MPs and MEPs in order to get on the ballot of members. In 2015 Corbyn relied on votes 'lent' to him by centrist MPs who didn't think he'd come close to winning. Having learned their lesson, no such lent votes would be offered for a Corbynite successor.

But if Labour does lose heavily in June, the actual number of nominations the Corbynites would need to get a candidate on the ballot would drop - from 15% of Labour's current 229 MPs and 20 MEPs to 15% of fewer MPs and MEPs.

And then the question would be how many radical left-wing MPs survive the electoral onslaught, and how many other left-wingers are willing to throw their lot in with them. For every six-to-seven seats Labour lose at the general election, the Corbynites need one fewer MP's nomination. It's not easy, but if they can secure safe seats for their favoured sons, it could happen. Here's how.

Labour lefties - gotta catch 'em all!

Let's split the potential support base into different groups:

Core Corbynites - allies from the Old Left, going back decades:

Dennis Skinner

Diane Abbott

Jeremy Corbyn - departing leaders are allowed to nominate a successor; let's assume he uses it, unlike Ed Miliband in 2015

John McDonnell

Solid left - other left-wingers who nominated Corbyn in 2015:

Grahame Morris

Kelvin Hopkins

Ronnie Campbell

Jon Trickett

Young left - left-wing MPs elected in 2015, who have backed Corbyn ever since:

Cat Smith

Imran Hussain

Kate Osamor

Rebecca Long-Bailey

Richard Burgon

Shadow ministers - left-wing and left-leaning MPs who didn't nominate Corbyn in 2015 but are reported to have backed him in the vote of confidence after the Brexit vote and now serve in his shadow frontbench team:

Andy McDonald

Angela Rayner

Barry Gardiner

Debbie Abrahams

Emily Thornberry

Ian Lavery

Gill Furniss - elected to parliament in May 2016, succeeding her deceased husband, Harry Harpham, who backed Corbyn in 2015

Peter Dowd

Bill Esterson

Carolyn Harris

Former allies - left-leaning MPs who left Corbyn's shadow frontbench but could plausibly back a left-wing successor:

Clive Lewis

Dawn Butler

Jo Stevens

Louise Haigh

Paul Flynn

Rachael Maskell

Clive Efford

Other left-leaners:

Ian Mearns - left-winger who backed Corbyn in the 2016 confidence vote

Margaret Greenwood - NHS campaigner who backed Corbyn in the 2016 confidence vote

Kate Hoey - pro-Brexit maverick leans left on some policy issues, backed Corbyn in the 2016 confidence vote

On top of those 33 sitting MPs, there are left-wing prospective candidates who could be elected in June, with Corbyn's team frantically trying to secure them vacant safe seats.

Newbies:

Katy Clark - former left-wing MP for North Ayrshire and Arran, hired as Corbyn's political secretary after losing out in the SNP landslide

Daniel Carden - left-wing aide to Unite leader Len McCluskey, linked with Liverpool Walton

Emma Hardy - candidate for Hull West and Hessle, local Unite-backed former teacher and official with the Socialist Education Association; not part of a Corbynite faction, but describes herself as a "democratic socialist"

Corbyn's allies have so far struggled to get his supporters accepted by constituency parties, with local or union-backed candidates preferred. Emma Hardy, who is not a Corbyn insider, was selected for Hull West ahead of leading Corbynite Sam Tarry. Katy Clark is linked with the vacant Rochdale candidacy, but may struggle against former Manchester Central MP Tony Lloyd.

If Rochdale and Liverpool Walton both select Corbynites, that's 36 possible nominations for a Corbynite. At present, candidates need the backing of 15% of Labour's 229 current MPs and 20 MEPs - in other words, 38 nominations. They would fall just short.

Apocalypse soon

But as noted earlier, a sharp fall in Labour MPs lowers the number of nominations the Corbynites need. Therefore the big question is how many seats Labour lose in June - and who survives the cull. Professor Tim Bale calculated that Corbynite MPs have larger majorities than centrists, although he used a narrower list of left-wingers than those named above. If centrist MPs are disproportionately hit by a Tory landslide, it becomes easier for the left to clear the 15% threshold - and vice versa.

Looking at the above list, Cat Smith and Margaret Greenwood are extremely vulnerable - they won their seats from the Tories in 2015 with small majorities that now seem almost impossible to defend. Clive Efford, sitting on a 6.2% majority in a seat with one of London's larger Ukip votes, also looks endangered.

The fortunes of others are harder to predict. Kate Hoey is vulnerable to a strong Lib Dem challenge due to her open support for Brexit. Jo Stevens is also at risk, having won her seat from Tim Farron's party two years ago.

The post-referendum switching of Ukip voters to the Conservatives puts Paul Flynn and Debbie Abrahams in danger. Clive Lewis and Rachael Maskell are also vulnerable, though they could mine substantial Green party support for votes to pull themselves through.

If, in a full-on meltdown, Labour is reduced to 150 seats and loses all nine of these MPs, the Corbynites would still have 24 left-wing MPs from the list above, plus Emma Hardy and whichever left-winger is inevitably parachuted into Liverpool Walton. That would be enough to get a Corbynite onto the ballot, though that candidate would need the backing of every single one of the survivors - John McDonnell probably wouldn't manage it.

But if Labour emerges with 170 seats, the left would need Lewis and Maskell to pull through - plus one more, which is why Corbyn's insiders are so desperate to secure safe seats for allies like Katy Clark.

How Corbynite is Corbynite?

This is Labour, so inevitably things get more complicated still. Of the MPs listed earlier, only those in the first three categories are nailed-on to back a Corbynite. MPs in the other groups are harder to predict, such as Clive Efford and Kate Hoey. These could opt for a centre left candidate - or even a Blairite, especially if she were the only woman on the ballot.

Much depends on who the candidate is. The two previous leadership candidates - John McDonnell and Diane Abbott - would surely fail to get anywhere near the required total. Their appeal is far too narrow and if Corbyn suffers a defeat, there's no reason even left-wing MPs would see a future in repeating the trick.

However, more moderate 'Corbynites' such as Emily Thornberry (a solid centre-left MP until 2015) and Angela Rayner (whose free school meals policy was widely praised by Labour centrists) could hoover up more support, potentially even beyond the Labour left.

The maths is the easy part...

Whatever happens, landing a Corbynite on the ballot will not be a cakewalk. Getting Clive Lewis and Kate Hoey to nominate the same candidate post-Brexit would be no easy task. A 'soft left' candidate such as Lisa Nandy could pull in enough support from left-wing MPs to kill off a Corbynite challenge. The actual hardcore Corbynites are very few in number - the old Campaign Group of socialist MPs is pretty much dead.

But for the right candidate, it is doable - the maths are tight, but workable. The question would then be whether the party membership flees to the centre in shell shock, holds out for a 'competent Corbynite', or simply blames everything on Blairites.

This would be the most important leadership election in the party's history. If McDonnell stood and won, swathes of centrist and centre-left MPs would inevitably defect, ripping the party in two. But a 'softer' Corbynite Labour leader would surely need to publicly detach themselves from the most electorally toxic aspects of Corbyn's leadership and legacy in order to make headway with the voters.

A Corbynite can succeed Corbyn, but Corbynism ultimately may not.

Chaminda Jayanetti is covering the general election for politics.co.uk. He tweets here.

The opinions in politics.co.uk's Comment and Analysis section are those of the author and are no reflection of the views of the website or its owners.