A majority of members of Britain’s biggest trade union, Unite, support a public vote on the final Brexit deal, according to a fresh poll.

The findings will pile pressure on the general secretary Len McCluskey – a close ally of Jeremy Corbyn – to “stand up for members” and revise his union’s policy on the contentious issue.

Crucially, the results also come ahead of Unite’s policy conference in Brighton next week with at least a dozen motions put forward by union branches on Brexit, including one on a fresh public vote.

According to the poll by YouGov, commissioned by the People’s Vote campaign, 57 per cent of members said they backed a public vote on Theresa May’s final Brexit deal while 34 per cent are opposed to the idea. Nine per cent said, “don’t know”.

Asked whether Unite union, which represents more than 1.4 million members, should campaign for a referendum on these terms, 49 per cent were in favour while 39 per cent were opposed.

Members polled also believed that Britain would be economically worse off if it left the single market after Brexit by a margin of 58 per cent to 21 per cent. Just over a quarter (26 per cent) replied that it would have “no real difference to me and my family”.

Mr McCluskey has previously refused to rule out a fresh referendum on Brexit but has echoed the views of senior shadow cabinet ministers who would rather have a general election should the prime minister’s deal be voted down in the Commons.

If his union does decide to throw its support behind a fresh referendum, however, the ramifications for the Labour party would be significant – Mr Corbyn would undoubtedly face renewed pressure to make a radical shift towards a public vote.

The Labour leader has already faced calls from his own supporters this week, as a new grassroots campaign, Labour for a People’s Vote, urged Mr Corbyn to support another referendum and avoid Ms May’s “kamikaze” Brexit.

According to Labour for a People’s Vote, activists in 60 Constituency Labour Party (CLP) groups have pledged to put forward a motion on the issue to both their local party and to the national conference in Liverpool later this year.

Pressed in the survey on whether members supported or opposed the approach by the Labour leadership towards Brexit, 52 per cent opposed and 29 per cent said they supported the party’s position.

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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. 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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. 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But the respondents said they held more trust in Mr Corbyn than Ms May in making the “right decisions” about Brexit.

“This is not about playing games in Westminster but about real lives that are going to be affected by Brexit,” said Baroness Margaret Prosser, an ex-president of the Trade Union Congress.

She said: “There are growing calls for a People’s Vote on the final Brexit deal and they go far beyond traditional party politics.

Lady Prosser – also a former deputy general secretary of the old TGWU which merged into Unite, continued: “I support people being given a democratic right to have their voice heard on Brexit before a final decision is taken to leave the EU.

“Unite has an opportunity to back that too this week – we should stand up for members and speak up for a People’s Vote.”