Nick Clegg risks losing his Sheffield Hallam seat at the 2015 General Election to Labour, according to a poll from Lord Ashcroft.
The survey, which questioned 1,000 people in the South Yorkshire constituency between 18 and 24 November, found that the Liberal Democrat leader was only three points ahead of Labour's candidate, Oliver Coppard, ahead of next May's vote.
The poll put the Liberal Democrats on 31%, Labour on 28%, the Conservatives on 19% and Ukip on 11%.
In contrast, Clegg won 53% of the vote in the 2010 General Election and the nearest contender was the Conservative candidate who secured 23%.
"I would be amazed if the Liberal Democrat leader ended up losing his seat, but remember he won 53% of the vote in Hallam at the height of Cleggmania," Ashcroft said.
The research also found that the Conservatives are only five points ahead of Ukip in Thanet South (34% vs 29%), where Nigel Farage will stand in 2015.
The study also found that there was "little good news" for Ed Miliband in Ashcroft's poll of Doncaster North.
Respondents said they trusted the prime minister and Chancellor George Osborne more over management of the UK economy when compared to Miliband and the Shadow Chancellor Ed Balls. (38% vs 35%).
"But it is not all bad. His constituents think he is performing nearly as well as Cameron," Ashcroft added.
"Asked how good a job each leader was doing on a scale from zero to 10, they awarded a mean score of 4.40 to the prime minister, and to 4.27 to their MP," Ashcroft said.
"On the whole they thought Farage was doing best, giving him 4.83. Still, nearly a quarter (24%) of Miliband's constituents thought he would make the best prime minister of the four, compared to only 23% who chose Cameron."
The figures come after a poll from YouGov for The Sun revealed that the Conservatives were one point ahead of Labour in the national polls (33% vs 32%).
On 1 December Lord Ashcroft issued a clarification and apology.
"The slightly more uncomfortable but nonetheless crucial side of transparency is that people can see when a mistake is made," Ashcroft said.
"Unfortunately that was the case last week in my poll of Doncaster North.
"I am grateful to Anthony Wells for bringing to my attention an error in the way this survey was weighted.
"A mistake at the data processing stage meant that the poll included too many Conservative voters and not enough Labour voters.
"This made opinion in Doncaster North look considerably less favourable towards Ed Miliband than it actually is."