The Liberal Democrats could be decapitated at the general election as Nick Clegg faces losing his Sheffield Hallam seat to Labour's candidate.
A poll from Survation, which questioned more than 1,000 residents between 22 and 26 of January and was commissioned by Unite, found that the Liberal Democrat leader was down 30% when compared to the 2010 general election.
The data showed that Labour candidate Oliver Coppard was on 33% in the constituency (up 17%), the Liberal Democrats were on 23%, the Tories on 22%, the Greens on 12% and Ukip on 9%.
If Clegg is deposed, it will be the first time in 70 years that a major party leader has been unseated in a British general election, and arguably the biggest electoral shock in the UK since 1935, when Labour leader Ramsay MacDonald was unseated.
The research also revealed that almost two thirds (64%) of Sheffield Hallam constituents oppose the inclusion of the NHS in the US-EU trade deal known as the Transatlantic Trade and Investment Partnership (TTIP).
"Clegg backed the Tories over the health sell-off and he's doing nothing to stop the irreversible privatisation of the NHS because of a dangerous trade deal called TTIP," Len McCluskey, the general secretary of Unite, told the Daily Mirror.
But a spokesperson for Clegg, who holds a majority of more than 15,000, said it was "hardly surprising" that a trade union-backed poll favours Labour, "given their total reliance on big money from the trade unions".
The figures come after a separate poll from Lord Ashcroft found that Labour could take a critical blow in Scotland at the general election as the party's campaign manager and shadow foreign secretary faces losing his seat.
Douglas Alexander, who represents Paisley and Renfrewshire South, would lose his place in the House of Commons with a 25% swing to the Scottish National Party (SNP), according to Lord Ashcroft.
The former Tory party deputy chairman, who surveyed more than 16,000 people, found that respondents' standard voting intention was 39% for Labour and 45% for the SNP, and their constituency voting intention was 40% for Labour and 48% for the SNP.
The long-awaited polling also revealed that former First Minister of Scotland Alex Salmond is set to unseat the Liberal Democrats in Gordon and return to Westminster, with a swing of 15.5% to the SNP in the constituency.