Trade unionists overwhelmingly back a fresh Brexit referendum, a survey has found, as Jeremy Corbyn consults them ahead of a possible shift in Labour policy.

Almost two-thirds of union members support a Final Say public vote, it showed – rising to more than three-quarters of those who backed Labour at the last general election.

They also want Labour to campaign for the UK to stay in the EU by a three-to-one margin and are three times more likely to vote for a Labour Party fully backing a referendum than deterred from doing so.

The results come at a crucial time, ahead of another crunch shadow cabinet meeting on Tuesday when Mr Corbyn will again come under huge pressure to come off the fence.

Delaying a decision last week, he said: “I will be hearing trade union views and then I want to set out our views to the public” – hinting at a major speech.

Jo Stevens, the secretary of the trade union group of Labour MPs and a supporter of the People’s Vote campaign, urged Mr Corbyn to listen to “the strong message”.

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“Labour’s official position is still too far behind that of our party members and voters, not to mention grassroots trade unionists who are the bedrock of our movement, she said.

The results showed “working people, trade union members” wanted a Final Say vote “just like his constituents do in Islington”, Ms Stevens added.

Peter Kellner, the former president of YouGov, which carried out the poll of 1,813 people, said members in all of the big three unions, Unison, Unite and GMB, were speaking with one voice.

“Although views vary slightly, clear majorities in all three unions back a new public vote and a Remain outcome,” he concluded.

The hopes of many Labour MPs of a fundamental shift to outright support for a second referendum came to nothing last week, when the shadow cabinet meeting broke up without agreement.

Mr Corbyn alarmed those pressing for a commitment to campaign for Remain by saying any referendum ballot paper should contain “real choices for both Leave and Remain voters”.

Tom Watson has now accused Labour bosses of rigging an analysis of the party’s European elections disaster to block a shift to fully backing a second referendum.

Ahead of Mr Corbyn meeting trade union general secretaries, the poll found rank and file members:

* Back a People’s Vote by 64 to 33 per cent – and support staying in the EU by a margin of 71 to 29 per cent if it is staged;

* Want Labour to campaign for the UK to stay in the EU by 60 to 21 per cent – rising to 74 to 10 per cent among the party’s 2017 voters;

* Think Labour’s current position on Brexit is confusing or unclear by a margin of 81 to 16 per cent;

* Believe it is more important to have free trade than to control immigration by a margin 73 to 20 per cent; and