Labour is braced for a showdown over whether to back a referendum on any Brexit deal when the party’s governing body meets to agree its draft European elections manifesto on Tuesday.

Party sources suggested Labour was likely to agree a compromise option where it would support a referendum in order to prevent Theresa May’s Brexit deal or leaving without a deal, describing that wording as “the path of least resistance”.

However, a public drive for a stronger line has been led by the party’s deputy leader, Tom Watson, who has urged remain-supporting members to write to the national executive committee’s members, including Jeremy Corbyn.

More than 100 Labour MPs have written to NEC members to argue that Labour should use the election to campaign for a second referendum in any circumstances and more than 20 Labour MEP candidates have pledged to back a referendum and then campaign to remain in the EU.

On Monday, the Labour MPs behind the parliamentary drive for a confirmatory referendum on Brexit also wrote to the NEC urging it to use the European elections to campaign for a fresh poll regardless of whether a deal has been reached with the government.

The manifesto, drafted by Labour’s policy chief, Andrew Fisher, is expected to be presented to NEC members on Tuesday. A source close to the NEC said they expected a compromise would be reached which would commit the party to campaign for a referendum to stop a “Tory Brexit” and leave open the possibility of a fresh poll in other circumstances.

“That would not prevent MPs attaching a referendum as a condition on any Brexit deal that comes to parliament,” the party source said.

Labour MPs Phil Wilson and Peter Kyle, who have drafted an amendment to any future binding Brexit vote that would commit MPs to passing May’s withdrawal deal subject to a public vote, said that option had the most popular support in the party.

In their letter to the NEC on Monday the pair wrote that it was “an opportunity to hold the Tory government to account on its botched approach to Brexit”.

The letter said a confirmatory ballot was supported by 203 Labour MPs, including 110 from seats that had a majority leave vote three years ago and had been whipped by the Labour frontbench when MPs took part in indicative votes in parliament.

“If a ‘deal’ is implemented without first going to the people for confirmation, then in the months and years ahead, the public will have a right to say: ‘This isn’t the Brexit I voted for,’” the letter said.

“The public wants Brexit to be over. They are looking to the Labour party to resolve this Brexit crisis. The way to resolve this crisis is in a confirmatory ballot with the facts of the deal before the British people.”

Watson’s efforts to persuade NEC members to back his bid for a more explicit endorsement of a referendum have been backed by several key members but also sparked a public backlash.

Jon Lansman, an NEC member and the founder of the leftwing grassroots group Momentum, said the party’s conference motion on Brexit had agreed that any Tory deal should be put to a public vote.

However, another NEC member, Claudia Webbe, accused Watson of being divisive. “Supporting Jeremy Corbyn & the Labour party to achieve this to kick out the Tories should be your focus,” she tweeted.

A letter from MPs and MEPs calling for a public vote on any Brexit deal, organised by the Love Socialism, Hate Brexit group, reached 118 signatures on Monday night, meaning the majority of non-shadow cabinet MPs have now signed the letter, including key Corbyn allies Clive Lewis and Kate Osamor.

The group’s co-founder, Lloyd Russell-Moyle, the MP for Brighton Kemptown, said: “Our letter shows that this isn’t about any single faction in the Labour party. It’s about the whole party coming together around a shared vision.

“A clear commitment on a public vote on any deal must be the cornerstone of our manifesto. It is a compromise that can unite the whole party and our electoral coalition.”

Interventions from trade unions, who have representatives on the party’s NEC, are also likely to prove crucial. Unison, GMB and the TSSA are likely to push hard for a confirmatory referendum.

Sources said Unison’s head, Dave Prentis, is leaning towards putting a clear pledge before voters. Tim Roache, GMB’s general secretary, has reiterated his union’s position for a so-called people’s vote. “We have made our position crystal clear – it must be the public who have the final say on Brexit,” he said.

Party sources said they expected GMB to be one of the strongest voices at the meeting arguing in favour of a second referendum in any circumstances.

The TSSA general secretary, Manuel Cortes, said the party should “act on the overwhelming wishes of its members and voters by pledging to support a confirmatory public vote on any Brexit deal”.

However, the option to hold a referendum in all circumstances is likely to be strongly opposed by Unite, a powerful ally of Corbyn on the committee, and the CWU, the communication workers union, which last weekend confirmed union policy to oppose a second referendum carried by more than 90% of delegates.

The party’s youth representative on the NEC, Lara McNeill, has said she will oppose any efforts for a public vote.

“At a time when this country so desperately needs a general election, and with Westminster in such conditions of turmoil, I am not prepared to say that every option has been exhausted,” she wrote in a blog for Huffington Post.

“Nor do I think it would be wise to commit the party to putting remain on the ballot paper should such a time come when all other avenues to preventing a damaging Brexit have been closed off.”