Senior Labour figures have pushed the party significantly closer to backing a fresh Brexit referendum, suggesting support is now inevitable unless Theresa May drops her “red lines”.

A trio of shadow cabinet members piled pressure on Jeremy Corbyn by saying the party must stick by its pledge to “campaign for a public vote” if the prime minister holds firm and Labour fails to force a general election.

Keir Starmer, the shadow Brexit secretary, said backing for a Final Say referendum was the only “remaining option” if Labour’s own withdrawal plan is defeated, adding: “That is a very important commitment. And it is one we will keep.”

Emily Thornberry, the shadow foreign secretary, echoed the view, saying: “If she refuses a general election and to change her deal, then of course our policy is that we will go for a people’s vote.”

And Tom Watson, Labour’s deputy leader, speaking at the same conference, told a questioner urging quicker support for a referendum: “I am tempted to go there with you.”

The calls came after Mr Corbyn angered some Final Say supporters by saying Labour would only consider backing a new referendum if the UK was on the brink of the “disaster of no deal”.

They suspect him of planning to table repeat votes of no confidence to try and trigger an election as a device to avoid ever grasping the nettle of a further public vote.

Speaking to The Independent after his speech, Sir Keir declined to set a deadline for the dramatic policy shift, with events in parliament over the next two weeks impossible to predict.

But he said: “I am deeply conscious that there are only 69 days to go before the 29 March, therefore the window now is quite short.”

Sir Keir also vowed the decision would not be taken by a closed circle, saying: “It is very important that, firstly, we hear what everybody has to say and, secondly, that we do it in a united way.”

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He insisted he and Mr Corbyn were “united”, adding: “We discuss this on a regular basis. People are always trying to find differences but we stand together behind that motion [on when to support a referendum].”

The issue will come to a head after Monday, when MPs will be free to lay a string of amendments to the prime minister’s “next steps” statement, following the devastating defeat of her deal last week.

They will include Labour’s alternative plan, for a customs union, a “strong” single market relationship and protection of workers’, environmental and consumer standards.

There will also be a Final Say amendment, probably to be tabled by Conservative Sarah Wollaston, but it cannot pass the Commons without the support of Labour’s leadership.

Ms May appears to have abandoned attempts to find a cross-party consensus, ruling out any significant changes to her deal ahead of Monday’s statement.

Instead, she spent Friday meeting cabinet ministers – which only underlined the deep split between those urging compromise and those warning the Tory party will implode if she makes concessions.

On Saturday, Sir Keir told a conference there were only “two remaining options”, the first being the government accepting a “close economic relationship with the EU”, as Labour proposed.

“Secondly, as our conference motion sets out, the option of a public vote,” he said.

He added: “I know there is significant support for this in our membership, in many trade unions, among a number of Labour MPs... this has to be an option for Labour.”

Mr Watson added, on a second referendum: “That might be the only way that the insurance policy part of our conference resolution can help break the impasse in those Brexit negotiations.”

But Ms Thornberry warned that, if Labour ended up backing a public vote, it must not repeat the “dreadful mistakes of the Remain campaign”.

Earlier, John Major urged Theresa May to give her ministers free votes on all the Brexit options, along with other MPs, and relegate herself to being a “mediator” to solve the crisis.

The Commons had “killed” her deal and she must recognise that attempts to revive it with minor “tinkering” – while sticking to her strict “red lines” – were doomed to failure.

Calling for a radical “act of statesmanship”, the former Conservative prime minister said: “All party leaders would permit a free vote so we can get an honest representation of parliament.

“And that is in the prime minister’s interest for this reason – it’s the only way to get an absolutely honest answer from members of parliament.”