Sir Vince Cable had said the campaign for a second Brexit referendum has ”momentum that will now be very hard to stop” after political and non-political figures joined The Independent in calling for a public vote.

The Liberal Democrat leader said there was now a “very real possibility” that the government will be forced to call a vote on the final Brexit deal, and claimed “cheating” and “Russian state involvement” had undermined the result of the original referendum.

Support for a “People’s Vote” on the final Brexit deal has grown since The Independent launched its Final Say campaign to give the public the chance to decide whether they still want to leave the EU.

More than 390,000 people have signed the petition in just six days.

Sir Vince said the public was increasingly supportive of a referendum on the final Brexit deal, but warned pro-EU campaigners: ”Victory is not a foregone conclusion.”

Writing exclusively for The Independent, he said: “Big political ideas take time to germinate. The idea that the course of Brexit should now be decided by allowing the people to have the final say through a vote, with the option to remain in the EU, was until very recently regarded as improbable.

“The leaders of the Tory and Labour parties regarded it (and still do) as a serious heresy. Yet public opinion is inexorably moving in that direction.”

He added: “The endorsement by previously uncommitted statesmen (such as Sir John Major) and non-political figures (for example, Gary Lineker) has contributed to a momentum that will now be very hard to stop, the more so as the seemingly comfortable option of a ‘soft’ Brexit now looks almost unattainable.”

Raising doubts about the legitimacy of the original Brexit vote, he said: “There is, in addition, the mounting evidence that the referendum was contaminated by Russian state involvement in favour of Brexit, and by cheating.

“As a football fan, I am familiar with the cry of ‘we wuz robbed’ – and the belief that defeat can be blamed on the ‘blind referee’. But in this case the emerging evidence is sufficiently serious to question the legitimacy of the results.”

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

Senior figures from all of the main political parties have now backed calls for a Final Say on Brexit. As the campaign has gathered momentum, bookies revealed that the odds on a second vote have halved since the start of 2018.

A new poll by Sky News suggested 59 per cent of people would rather the UK remained in the EU than crashed out without a deal.

Sir Vince said several factors were behind the shift in public opinion, including increasing doubts that Theresa May will be able to secure a Brexit deal with Brussels.

He accused the prime minister of having made a “grievous error” in “setting out red lines which would later have to be crossed to get a sensible deal” and claimed her failure to build support for her Brexit vision means a referendum is the only way to settle the row over Britain’s relationship with the EU.

Ms May had hoped the plan agreed by ministers at Chequers earlier this month would help to break the deadlock in negotiations but it was widely opposed by many in her own party and quickly rejected by the EU. Sir Vince said the Chequers plan had been “shot to pieces by the cabinet even before Monsieur Barnier [the EU’s chief negotiator] fired a bullet into the corpse”.

Chuka Umunna and John Rentoul debate the possibility of another Brexit referendum

The Liberal Democrat leader also suggested the election of Donald Trump on a platform of “economic nationalism” had scuppered any hope of a “buccaneering, free trading ‘global Britain’” and given the EU the upper hand in negotiations.

Joining other senior figures such as Tony Blair, former Tory cabinet ministers Justine Greening and Dominic Grieve and Green Party co-leader Caroline Lucas in backing The Independent’s campaign, Sir Vince said pro-EU campaigners “need to prepare” for a second referendum.

He said: “I do not pretend that having a vote on the final deal will be universally popular. The issue divides families and friendships and there will be resistance to exposing those divisions again. But the alternative – of drifting into a form of Brexit that will leave a growing majority, the next generation, damaged by the outcome – is not attractive either.

“There is now a real possibility that a vote on the final deal will happen. Those of us who will be campaigning to stay in the EU, albeit an EU that is reformed and improved, will need to prepare. Victory is not a foregone conclusion. The proponents of leaving will seek to whip up British nationalism. Nor will they necessarily accept the result.