Labour members are changing their mind about Jeremy Corbyn.

Polling commissioned by Election Data’s Ian Warren reveals that 50 per cent of Labour members want their leader to stand down before the general election,compared with 44 per cent who would like him to stay.

The results of the YouGov poll also suggest a sharp drop in Corbyn’s approval rating among Labour members over the course of a year. His net approval rating was 55 per cent in February 2016 – it is now just 17 per cent:

On @pestononsunday Allegra put up an approval chart for Mr Corbyn. Here are the underlying changes: @YouGov pic.twitter.com/IGevPlvmQ1 — Election Data (@election_data) March 5, 2017

A whopping 63 per cent of Labour members believe the party is not doing enough to hold the government to account on Brexit, and 53 per cent believe Corbyn has handled Labour’s position on the issue badly (43 per cent believe he’s handled it well).

Plus, 41 per cent of Labour members blame Corbyn for Labour’s defeat in the Copeland by-election two weeks ago – higher than the proportion who blame any other factor.

I asked @UKLabour members who they thought was responsible for the by-election defeat in Copeland. They said this: pic.twitter.com/1so7iBC7GA — Election Data (@election_data) March 5, 2017

This comes on top of the news last week that Labour has lost 26,000 members since last summer. More than 15,465 of these have left since mid-December – including the 7,000, as revealed by my colleague Stephen, who left following Corbyn’s three-line whip to vote for Article 50.

This shift in opinion of the Labour leader is giving Corbynsceptics reasons to be cheerful. But it doesn’t mean Corbyn wouldn’t win another leadership contest.

First, look at the rest of Election Data’s polling. When asked how they would vote if there were another leadership election, Labour members put Corbyn 15 points ahead of their second most popular candidate, Yvette Cooper:

I asked @UKLabour members which three or four potential candidates they would consider voting for in a future leadership election: pic.twitter.com/GsDtE32GEw — Election Data (@election_data) March 6, 2017

Corbyn also comes eight points ahead of Cooper as the “most credible Prime Minister”, according to Labour members.

A majority of Labour members would still definitely or probably vote for Corbyn again, compared to those who would definitely not or probably not (52 per cent to 46 per cent).

I asked @UKLabour members how likely or unlikely it was that they would vote for Mr Corbyn in a future leadership contest. They said: pic.twitter.com/2p9YLxygyr — Election Data (@election_data) March 6, 2017

As long as Jeremy Corbyn is leader, he will remain the party’s most popular candidate. He won the last leadership election by 119,980 votes overall, and by 51,256 among members. Even with the recent loss of members and a drop in approval ratings, the margin for another Corbyn victory remains.

What could prompt Labour members to turn on him? It's hard to say. Although the majority of the selectorate last year were pro-Remain (while Corbyn is a Eurosceptic), he still won against a soft left candidate who was calling for a second referendum.

In light of this, it’s difficult to see what it would take to turn the membership against him. The polling shows that the EU is the highest priority (joint with health at 66 per cent) among Labour members, and even then it’s not enough to turn the party wholesale against him.

However, if Corbyn were swapped for another candidate representing his strand of politics – as disillusioned supporters such as Owen Jones have urged – this would not guarantee a win for the hard left. The polling shows that, if Corbyn weren’t on the ballot, his shadow chancellor and ally John McDonnell would only come joint top with Cooper, rather than triumphing Corbyn-style.Other mooted Corbynite successors such as Rebecca Long-Bailey, Clive Lewis and Angela Rayner either hardly register or fall behind more “moderate” candidates.

I asked @UKLabour members which three or four potential candidates they would consider voting for if Mr Corbyn stood down. They said: pic.twitter.com/4DLPMkd39l — Election Data (@election_data) March 6, 2017

Without a guarantee that a successor candidate would win, or even make it onto the leadership ballot paper, it seems unlikely that Corbyn would step down. What is most important to him and his allies is to ensure the party’s future is in the hands of the Corbynite left – something that looks tricky without Corbyn remaining at the helm.

As I found in my report into whether Corbyn is losing enough support to destabilise his leadership, the hard left and Momentum would most likely fight successfully to keep Corbyn in power, especially if he were challenged by another faction of the party. The centrists know this, so will not be mounting another challenge at this point. And the Corbynites won’t be pursuing a successor “swap” until they come up with a candidate who would secure victory for their wing of the party.