A string of senior shadow ministers are advocating a new public vote, alongside MPs from the left and right of the party, buoyed by a groundswell of support from the membership.
The Independent understands Labour is now beginning the process of drawing up its manifesto with those wanting to give the public a final say on Brexit pushing the leader to make a strong bid for the Remain vote on polling day.
Mr Corbyn’s team is currently engaged in talks with the Conservatives in an effort to find a Brexit compromise deal that can enjoy majority support in the House of Commons, with a referendum having been discussed during the negotiations.
The leader’s office emphasised that decisions on the manifesto were yet to be discussed, with the party simultaneously defending its majorities against the pro-Remain Change UK party run by Labour defectors and Nigel Farage’s new Brexit Party.
One shadow cabinet source told The Independent: “We can’t credibly agree to any deal unless there is a confirmatory referendum attached to it.
“We should be telling people about that, the support is there to be had.”
The European elections are set to become a rerun of the 2016 referendum campaign with parties positioning themselves along the Brexit spectrum from Leave to Remain.
A source in the Labour leader’s office said it was too early to have a manifesto for the poll on 23 May, and said that the offering would be decided in the same way as for previous elections.
But other party sources said discussions had already happened on how the party should approach the issue of Brexit and a referendum.
Supporters argue a failure to back a new referendum would be seen as a betrayal by party members who voted Remain, particularly after the party’s conference backed one if a general election could not be achieved.
Shadow foreign secretary Emily Thornberry, shadow chancellor John McDonnell, shadow Brexit secretary Sir Keir Starmer and shadow home secretary Diane Abbott have led the push for a new vote, along with out-of-favour deputy leader Tom Watson.
Mr McDonnell has said that a new public vote could be a way of entrenching support for any deal reached in talks with the government.
Ms Thornberry recently sent a letter to MPs that it would be “in breach of the decision made unanimously by conference” for there not to be a confirmatory referendum held.
Unions are also backing a new vote, with Unison recently voting in favour of one. TSSA union general secretary and a Corbyn ally Manuel Cortes told The Independent: “Overwhelming numbers of Labour voters want an end to the Brexit madness. Labour must give these people hope. We must promise to put any deal back to the people for a confirmatory vote.
“I really fear that if we don’t pledge this in our European election manifesto, we will be squeezed by the likes of the Greens and the SNP, and some of our voters will simply stay at home.”
The left-wing MP and shadow treasury minister Clive Lewis added: “The world is watching, and Labour needs to stand its ground against the Tories and against the centrist parties.
“And we have to be clear about the role of Europe in that, by arguing for Remain and transform. That’s why I’m glad that Labour’s policy has shifted in recent weeks and we can go into these elections arguing for a confirmatory public vote.”
His colleague, the Labour MP Lloyd Russell-Moyle, said: “The PES [Party of European Socialists] manifesto offers a transformative left-wing programme for the EU. We need to adopt it and fight for it – and that means a Remain and reform message, and a confirmatory public vote.”
But while some inside the leader’s office see the ground to be gained in taking a stronger line on a referendum, there is still nervousness from others close to the leader and outright opposition from some shadow cabinet members.
Party chair Ian Lavery has twice defied the Labour whip to abstain on votes in which the front bench backed a new referendum on Brexit and is said to have warned Mr Corbyn he could go down in history as the leader who “split the party”.
At the launch of Mr Farage’s new Brexit Party on Friday, the ex-Ukip leader said he expected to steal voters who backed Leave in 2016 from the Labour Party, which he called “pretty much pro-Remain”.
Meanwhile, Mr Corbyn’s party is also under pressure from the referendum-backing Change UK, set up by ex-Labour MP Chuka Umunna and a handful of other defectors in protest over antisemitism and their former party’s Brexit stance.
Both Mr Farage’s group and Change UK are expected to try to use the European elections to break through and challenge the dominance of the established Westminster parties.
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