Pledging to give the British people a final say on Brexit would see a surge in Labour support that would carry it to the brink of government, according to two separate new polls.

One by YouGov found promising a People’s Vote referendum would mean Jeremy Corbyn’s party takes an additional 1.5 million votes, potentially gaining dozens of commons seats.

A second unconnected study by ICM of specific constituencies indicated such a pledge would see Labour win enough votes to hold and make gains in marginal constituencies – even in those that backed leaving the EU.

It comes as Theresa May’s push to win support for her Chequers Brexit deal in Europe was thrown into turmoil after all 27 EU member state leaders dashed her hopes of progress and agreed it “will not work”.

Earlier in the day as the prime minister attempted to persuade them of its merits, some called for the British public to be given a fresh vote on Brexit as the options become clear.

The Independent has launched its own campaign for a Final Say referendum on the final Brexit deal, with more than 800,000 having signed the petition so far.

But the new data from two major pollsters sheds light specifically on the impact that backing a new referendum would have on Mr Corbyn’s electoral prospects, with the issue set to dominate Labour’s annual conference starting this weekend.

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Ex-president of YouGov Peter Kellner said his former organisation’s poll, commissioned by the People’s Vote campaign, “leaves no doubt that by backing a popular vote on Brexit, the party would end up making significant gains in votes and seats”.

It surveyed a weighted sample of the population numbering more than 10,000 people between 28 August and 4 September, with half saying the EU is the single biggest issue facing Parliament.

[This] leaves no doubt that by backing a popular vote on Brexit, the party would end up making significant gains in votes and seats Peter Kellner, ex-president of YouGov

Of this group some 37 per cent – equivalent to 7.4 million voters – said they would “definitely” vote Labour or be “more likely” to if the party backs a new vote.

Once those who were already Mr Corbyn’s backers are excluded, along with those who said that despite being more attracted to Labour they would still vote for another party, the proportion left represented 1.75 million non-Labour voters who said they would swing to the party if it backed a new referendum.

Mr Kellner went on: “What about voters who might desert Labour? A substantial minority of Labour supporters voted Leave in 2016. Many Labour MPs fear that support for a referendum could cost them votes at the next election.

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“YouGov’s figures do not bear this out. Of the YouGov respondents who currently support Labour and voted Leave in the Brexit referendum, only 6 per cent put Brexit at the top of their concerns and say they would not, or be less likely to, vote Labour if the party backed a popular vote.

“This is just two per cent of all Labour supporters, or just over 200,000 voters in all.”

He explained that once these voters were subtracted from those gained by a pledge to back a new referendum, the net increase is some 1.5 million votes.

Mr Kellner added: “Like all such hypothetical exercises, different ways of asking the questions and doing the sums will yield different results.

“But the nine-to-one gulf between the non-Labour target voters and the at-risk Labour supporters leaves no doubt that by backing a popular vote on Brexit, the party would end up making significant gains in votes and seats. In a tight general election, it could make the difference between returning to government and remaining in opposition.”

With those figures layered on the whole country, Labour would stand to gain around 60 seats across the UK.

People's Vote march – demanding vote on final Brexit deal Show all 30 1 /30 People's Vote march – demanding vote on final Brexit deal People's Vote march – demanding vote on final Brexit deal Mandatory Credit: Photo by Guy Bell/REX (9725259aq) Marching down Whitehall - People's March for a People's Vote on the final Brexit deal. Timed to coincide with the second anniversary of the 2016 referendum it is organised by anti Brexit, pro EU campaigners. People's March for a People's Vote, London, UK - 23 Jun 2018 Guy Bell/REX Rex People's Vote march – demanding vote on final Brexit deal Demonstrators carry banners and flags as they participate in the People's March demanding a People's Vote on the final Brexit deal, in central London on June 23, 2018, the second anniversary of the 2016 referendum. Tens of thousands of people demonstrated in London on Saturday calling for a second vote on Britain's departure from the European Union. / AFP PHOTO / Niklas HALLE'NNIKLAS HALLE'N/AFP/Getty Images NIKLAS HALLE'N AFP/Getty Images People's Vote march – demanding vote on final Brexit deal A young protestor shouts as she takes part in the People's Vote demonstration against Brexit Getty Images People's Vote march – demanding vote on final Brexit deal A woman holds a placard as she joins EU supporters, calling on the government to give Britons a vote on the final Brexit deal, participating in the 'People's Vote' march in central London, Britain June 23, 2018. REUTERS/Henry Nicholls HENRY NICHOLLS Reuters People's Vote march – demanding vote on final Brexit deal epa06833888 Pro-EU demonstrators take part in a People's March anti-Brexit rally in Parliament Square in London, Britain, 23 June 2018. Protesters are calling for a referendum on the final deal. The protest is taking place on the second anniversary of the Brexit referendum. EPA/ANDY RAIN ANDY RAIN EPA People's Vote march – demanding vote on final Brexit deal A protester's pro-EU t-shirt EPA People's Vote march – demanding vote on final Brexit deal epa06833892 A pro-EU demonstrator waves a European Flag during a People's March anti-Brexit rally in Parliament Square in London, Britain, 23 June 2018. Protesters are calling for a referendum on the final deal. The protest is taking place on the second anniversary of the Brexit referendum. EPA/ANDY RAIN ANDY RAIN EPA People's Vote march – demanding vote on final Brexit deal Demonstrators carry banners and flags as they participate in the People's March demanding a People's Vote on the final Brexit deal, in central London on June 23, 2018, the second anniversary of the 2016 referendum. Tens of thousands of people demonstrated in London on Saturday calling for a second vote on Britain's departure from the European Union. / AFP PHOTO / Niklas HALLE'NNIKLAS HALLE'N/AFP/Getty Images NIKLAS HALLE'N AFP/Getty Images People's Vote march – demanding vote on final Brexit deal epa06833960 Tens of thousands of people march through London during a People's March anti-Brexit demonstration in London, Britain, 23 June 2018. Protesters are calling for a referendum on the final deal. The protest is taking place on the second anniversary of the Brexit referendum. EPA/ANDY RAIN ANDY RAIN EPA People's Vote march – demanding vote on final Brexit deal Leader of the Liberal Democrats, Vince Cable speaks during the People's March demanding a People's Vote on the final Brexit deal, in central London on June 23, 2018, the second anniversary of the 2016 referendum. Tens of thousands of people demonstrated in London on Saturday calling for a second vote on Britain's departure from the European Union. / AFP PHOTO / Niklas HALLE'NNIKLAS HALLE'N/AFP/Getty Images NIKLAS HALLE'N AFP/Getty People's Vote march – demanding vote on final Brexit deal epa06833964 A young pro-EU demonstrator takes part in a People's March anti-Brexit rally in Parliament Square in London, Britain, 23 June 2018. Protesters are calling for a referendum on the final deal. The protest is taking place on the second anniversary of the Brexit referendum. EPA/ANDY RAIN ANDY RAIN EPA People's Vote march – demanding vote on final Brexit deal Gina Miller and Caroline Lucas EPA People's Vote march – demanding vote on final Brexit deal epa06834044 Tens of thousands of people march through London during a People's March anti-Brexit demonstration, in London, Britain, 23 June 2018. Protesters are calling for a referendum on the final deal. The protest is taking place on the second anniversary of the Brexit referendum. EPA/ANDY RAIN ANDY RAIN EPA People's Vote march – demanding vote on final Brexit deal epa06833264 Thousands of people march through London during a People's March anti Brexit demonstration in London, Britain, 23 June 2018. Protesters are calling for a referendum on the final deal. The protest is taking place on the second anniversary of the Brexit referendum. EPA/ANDY RAIN ANDY RAIN EPA People's Vote march – demanding vote on final Brexit deal Tens of thousands of people march through London EPA People's Vote march – demanding vote on final Brexit deal epa06833265 Thousands of people march through London during a People's March anti Brexit demonstration in London, Britain, 23 June 2018. Protesters are calling for a referendum on the final deal. The protest is taking place on the second anniversary of the Brexit referendum. EPA/ANDY RAIN ANDY RAIN EPA People's Vote march – demanding vote on final Brexit deal Demonstrators at the People's Vote March Getty People's Vote march – demanding vote on final Brexit deal 'Two months too young to decide on my future' REUTERS People's Vote march – demanding vote on final Brexit deal Crowds taking part in the People's Vote march for a second EU referendum at Trafalgar Square in central London. PRESS ASSOCIATION Photo. Picture date: Saturday June 23, 2018. See PA story POLITICS Brexit. Photo credit should read: John Stillwell/PA Wire John Stillwell PA People's Vote march – demanding vote on final Brexit deal A young girl joins in the march PA People's Vote march – demanding vote on final Brexit deal An EU flag is draped across the statue of Winston Chruchill in Parliament Square REUTERS People's Vote march – demanding vote on final Brexit deal Demonstrators gather prior to the start of the People's March demanding a People's Vote on the final Brexit deal, in central London on June 23, 2018, on the second anniversary of the 2016 referendum. / AFP PHOTO / Niklas HALLE'NNIKLAS HALLE'N/AFP/Getty Images NIKLAS HALLE'N AFP/Getty Images People's Vote march – demanding vote on final Brexit deal Vince Cable MP, Pro-EU campaigner Gina Miller, Tony Robinson and Caroline Lucas MP join with crowds PA People's Vote march – demanding vote on final Brexit deal Crowds gather on Pall Mall in central London, during the People's Vote march for a second EU referendum. PRESS ASSOCIATION Photo. Picture date: Saturday June 23, 2018. See PA story POLITICS Brexit. Photo credit should read: John Stillwell/PA Wire John Stillwell PA People's Vote march – demanding vote on final Brexit deal Crowds gather on Pall Mall PA People's Vote march – demanding vote on final Brexit deal A man resembling Britain's Foreign Secretary Boris Johnson, joins EU supporters Reuters People's Vote march – demanding vote on final Brexit deal EU supporters, calling on the government to give Britons a vote on the final Brexit deal, participate in the 'People's Vote' march in central London, Britain June 23, 2018. REUTERS/Henry Nicholls HENRY NICHOLLS Reuters People's Vote march – demanding vote on final Brexit deal People gather in Trafalgar Square REUTERS People's Vote march – demanding vote on final Brexit deal Pro-EU campaigner Gina Miller and Tony Robinson PA People's Vote march – demanding vote on final Brexit deal EU supporters, calling on the government to give Britons a vote on the final Brexit deal, participate in the 'People's Vote' march REUTERS

The ICM poll, separately commissioned by the group Represent Us, drilled down into specific constituencies by polling in 107 marginal seats across the UK with a majority of less than 3,500.

Across the 82 seats in England and Wales it found Labour would leapfrog the Tories in vote share with a pledge to back the new vote, going from a point behind in 2017 to a point in front, down in large part to stealing support from the Liberal Democrats.

That would indicate Labour holding its 35 most marginal seats in England and Wales and winning a further 16 from the Conservatives – despite at least 38 of these having backed Leave in 2016.

Backing a new referendum would also allow Labour to minimise potential losses against a dominant SNP in Scotland, according to the ICM data.

Dozens of motions have been tabled ahead of Labour’s conference in Liverpool in a bid to get the party to vote on backing a new referendum on Brexit, with several unions having already thrown their weight behind the idea in the run up.

There is also set to be a rally for a People’s Vote on Sunday in Liverpool right outside the party’s main conference event.

The Independent understands that the leadership will likely stick to its commitment to keep the option of a vote on the table, without giving explicit support to one.

Labour MP for Tottenham David Lammy urged his party to back a new referendum, saying: “What these figures show is that supporting a People’s Vote is also the right thing for the party to do if we want to win a general election.