Jeremy Corbyn has been accused of a “stitch-up” to avoid a conference defeat that would force him to support Remain in a fresh Brexit referendum.

A new policy statement, likely to be agreed on Sunday, would push back a decision on Labour’s stance to next year.

The party would wait until a “sensible” withdrawal deal had been negotiated within three months of winning a general election.

Only then would Labour decide its stance at a second referendum to be held within a further three months – possibly next May, if Boris Johnson holds a snap election in November.

As the party’s conference begins in Brighton, pro-EU MPs and activists protested that the delay was a clear attempt to stop them forcing Mr Corbyn to abandon his plans to 'stay neutral' in another referendum.

They had vowed to force an immediate showdown, armed with the 90 per cent of local party motions in favour of Remain.

Critically, because the policy statement comes from the ruling national executive committee (NEC), it will – if passed – strike out those other 81 activist options.

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Clive Lewis, a Labour Treasury spokesperson, said: “This move is just plain wrong. How can this be defended?

“Here we are, with a leadership apparently determined to shut down democratic debate on the crucial issue of the day, probably relying on union bloc votes to outvote the members.”

And Lloyd Russell-Moyle, a pro-EU backbencher, said: “This conference is our one chance before an election to get out of the fudge – we cannot allow that to be taken away from us in some procedural stitch-up.”

Two senior shadow cabinet members piled further pressure on their leader with strong pro-Remain speeches to a 5,000-strong People's Vote rally to mark the start of the conference.

Emily Thornberry, the shadow foreign secretary – sporting an EU flag – insisted “members must have their voice and the members must be heard, because this is what democracy looks like”.

“Whatever terms are agreed by which we leave the European Union, by whatever government, no matter what it says, we must make sure that there's a second referendum, we must make sure that Remain is on the ballot paper, we must make sure that Labour campaigns for Remain – and not just that, but that that we lead the campaign to Remain,” she urged Mr Corbyn.

To huge cheers, Ms Thornberry asked the rally: “If we believe in internationalism and socialism, why on earth would we back Brexit?”

Keir Starmer, the shadow Brexit secretary, told the crowd: “A year or so ago I wasn't sure that a referendum was the right way out, but now I'm utterly convinced it's the only way out.

“When that time comes, I will campaign for Remain alongside millions of other people in this country because it's not just a technical question of whether you want to be in or out of the EU, it's about what sort of country you want to be.”

The fresh controversy blew up within minutes of the bitter row over the attempt to topple Tom Watson being settled with a victory for the deputy leader and Corbyn critic.

The new clash sets the scene for a repeat of the marathon five-hour “compositing” meeting at last year’s Labour conference, which ended in Brexit policy being fudged.

However, the NEC statement will trump whatever that composite meeting decides – unless it is defeated later in the week on the conference floor.

Mr Lewis called for that to happen if necessary, adding: “If it passes, delegates should mobilise to vote against the NEC statement so the Brexit motions can be heard and democratically debated.”

Earlier, Ms Thornberry split with Mr Corbyn by calling for Labour to allow a Johnson-secured Brexit deal to pass – provided the public has the Final Say in a referendum.

The shadow foreign secretary became the highest-profile supporter of the so-called Kyle-Wilson plan, put forward by two Labour backbenchers.

“I think it’s something we would have to consider. We would have to consider it seriously,” Ms Thornberry said.

She also criticised Mr Corbyn’s intention to stay neutral in a fresh referendum, saying: “I think it wouldn’t be right for Labour to have no opinion on such a big decision.”

The leadership’s blueprint would see a one-day special conference decide – eventually – Labour’s campaigning position, putting it in the hands of the unions and grassroots.