Tom Watson has said a second referendum is the “only way” to unite the country and it would be “inconceivable” to not include the plan in a Labour election manifesto.

As speculation mounts over whether Theresa May will send Britons to the ballot box, Mr Watson said Jeremy Corbyn has put the party on an “election footing”, so it can field candidates in both a snap poll and possible European elections in May.

The deputy Labour leader said his party had seen a “boost in the polls” through its support for a second referendum and urged Labour to unite around the strategy as a way to hammer the Tories.

It comes as the prime minister is locked in talks with advisers over whether to bring back her Brexit deal this week, after it was voted down for the third time on Friday.

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(AP Photo/ Kirsty Wigglesworth) Kirsty Wigglesworth AP Opposing protesters flock to parliament on would be date of Brexit A pro-Brexit protester holds a sign next to a statue of Winston Churchill at the March to Leave demonstration in London, Britain March 29, 2019. REUTERS/Toby Melville TOBY MELVILLE Reuters Opposing protesters flock to parliament on would be date of Brexit Brexit demonstrators in Parliament Square in Westminster, London. PRESS ASSOCIATION Photo. Picture date: Friday March 29, 2019. See PA story POLITICS Brexit. Photo credit should read: Jonathan Brady/PA Wire Jonathan Brady PA Opposing protesters flock to parliament on would be date of Brexit Pro-Brexit protesters hold signs and wave flags at the March to Leave demonstration in London, Britain March 29, 2019. REUTERS/Toby Melville TOBY MELVILLE Reuters Opposing protesters flock to parliament on would be date of Brexit epa07471421 Pro-Brexit protesters gather outside of the Parliament for Nigel Farage's 'March to Leave' in London, Britain, 29 March 2019. MPs rejected Prime Minister's May EU withdrawal agreement earlier in the day. EPA/NEIL HALL NEIL HALL EPA Opposing protesters flock to parliament on would be date of Brexit A Brexit supporter sips a can of Stella in protests outside of the Houses of Parliament AFP/Getty Opposing protesters flock to parliament on would be date of Brexit Dedicated anti-Brexit campaigner Steve Bray and likewise pro-Brexit campaigner Joseph Afrane go head to head near the Houses of Parliament AFP/Getty Opposing protesters flock to parliament on would be date of Brexit A pro-Brexit marching band in Parliament Square Getty Opposing protesters flock to parliament on would be date of Brexit Remain supporters wave EU flags from a bus in Parliament Square PA Opposing protesters flock to parliament on would be date of Brexit A Brexit supporter shouts slogans outside parliament EPA Opposing protesters flock to parliament on would be date of Brexit A Brexit supporter protests outside parliament Reuters Opposing protesters flock to parliament on would be date of Brexit A Brexit supporter protests outside of the Houses of Parliament Getty Opposing protesters flock to parliament on would be date of Brexit Brexit supporters protest outside of the Houses of Parliament REUTERS Opposing protesters flock to parliament on would be date of Brexit A pro-Brexit flag is waved in Parliament Square AP Opposing protesters flock to parliament on would be date of Brexit The March to Leave nears the Houses of Parliament Reuters Opposing protesters flock to parliament on would be date of Brexit A Brexit protester holds a sign outside parliament EPA Opposing protesters flock to parliament on would be date of Brexit Brexit supporters carry the coffin of democracy AFP/Getty Opposing protesters flock to parliament on would be date of Brexit Brexit supporters march outside parliament AFP/Getty Opposing protesters flock to parliament on would be date of Brexit Brexit supporters take part in the March to Leave protest in London PA Opposing protesters flock to parliament on would be date of Brexit Brexit supporters protest outside parliament AFP/Getty Opposing protesters flock to parliament on would be date of Brexit A Brexit supporter holds a sign outside the Houses of Parliament Getty Opposing protesters flock to parliament on would be date of Brexit A man holds satirical paintings of politicians Reuters Opposing protesters flock to parliament on would be date of Brexit An pro-Brexit float on the March to Leave march in London Reuters Opposing protesters flock to parliament on would be date of Brexit Far-right activist Tommy Robinson addresses protesters outside the Houses of Parliament Getty Opposing protesters flock to parliament on would be date of Brexit A Brexit supporter outside the Houses of Parliament Reuters Opposing protesters flock to parliament on would be date of Brexit A Tommy Robinson supporter arrives at the Houses of Parliament Getty Opposing protesters flock to parliament on would be date of Brexit A jogger gestures rudely at a Brexit supporter outside of the Houses of Parliament AFP/Getty Opposing protesters flock to parliament on would be date of Brexit A Brexit supporter outside the Houses of Parliament PA

After the defeat, Ms May told MPs there were “grave” implications and sparked panic among Tories when she warned they were “reaching the limits of this process in this house” – a hint at an early general election.

It also comes as a viral petition urging the government to halt Brexit attracted more than six million signatures.

Mr Watson told the BBC’s Andrew Marr Show: “We need to move beyond Brexit but it seems to me the only way we can do that is to have a people’s vote.

“A people’s vote is the solution not an option. It’s the way we can move the country on.”

Mr Watson said he had spoken to the Labour leader on Saturday about election preparations, and he was preparing to engage with the party’s ruling body on its plans.

Asked if a second referendum would be in the manifesto, the shadow culture secretary said: “Obviously I don’t write Labour’s manifesto, I am one bloke around a table.

“But it seems to me to be inconceivable that if there was a general election tomorrow – and we hope there will be, we have been calling for one for months – that a people’s vote won’t be in the manifesto.”

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It is understood that Labour’s manifesto has not yet been written.

MPs are preparing to take control of the Commons timetable on Monday for indicative votes on different Brexit scenarios, after the first round of votes failed to reveal a clear way forward.

Labour would have to see what amendments are selected for the second stage of the Brexit indicative votes before revealing its voting intentions, Mr Watson said.

But he added: “It seems to me that parliament, certainly Labour MPs, are coming together with an emerging consensus that whatever that deal looks like – and we understand there has to be compromises – if it’s underpinned by a people’s vote that is the way we can bring the country back together.”

A Labour Party spokesperson said: “In line with Labour’s policy and conference decision, we will continue to seek a majority in parliament for a close economic relationship with the EU to break the deadlock or a public vote to avoid a damaging Tory Brexit or a no-deal outcome.

“If and when a general election is called, our manifesto will be decided through our party’s democratic policy-making processes in the usual way, which includes the Clause V meeting of MPs, trade unions and affiliates, councillors and party members.”

Elsewhere, shadow foreign secretary Emily Thornberry signalled that Labour would make another attempt to trigger a confidence vote in the government but did not specify when.

She said the prime minister was “out of control”, adding: “Even with just days to go she is just saying, ‘It is my deal or no deal.’

“That is not meaningful, that is not democracy. That is Theresa May stamping her feet and saying, ‘I want this, no one else is allowed to do anything.’

“No wonder she is in trouble. She is out of control. She is not listening to anyone. No one knows what it is that she is going to do next. I think her judgement has been undermined.”

She told Sky News’ Sophy Ridge on Sunday that it was “likely” Britain would leave the EU under a Labour government, although there was a strong case for a second referendum.