Ousting of Lib Dem leader could slash chances of party forming second coalition with Conservatives in event of hung parliament

Nick Clegg has admitted that he has been spending at least two days a week campaigning in his Sheffield constituency amid fears he could lose it to Labour.

The Liberal Democrats leader had a majority of more than 15,000 in Sheffield Hallam in 2010, but the collapse in support for his party, especially among students, has raised the possibility that Labour could pull off a surprise win in the seat.

A poll by Lord Ashcroft last month put Clegg just three points ahead of Labour (31% v 28%). That result was based on a question asking respondents to think about their own constituency and how they would vote there. When people were first asked a standard question about voting intention, without reference to the constituency, Labour was ahead of the Lib Dems by one point (28% v 27%).

At the general election, Clegg had 53% of the vote, ahead of the Conservatives on 23% and Labour on 16%.

Sheffield Hallam does not feature on Labour’s standard list of target seats, but Oliver Coppard, its candidate, has been running a high-profile campaign against Clegg and Tom Watson, Labour’s former campaign coordinator, told the Times that the seat was “winnable” for the party.

“I have never encountered such animosity on the doorstep against an incumbent MP – particularly one as high-profile,” said Watson, who has visited the constituency recently. “There are two issues that come up time and again: his position on tuition fees and Sheffield Forgemaster, which has not been forgotten.”

Labour has refused to comment on claims that it is making a special effort in Sheffield to unseat Clegg, but his removal could reduce the chances of the Lib Dems forming a second coalition with the Conservatives in the event of a hung parliament.

Clegg would be more open to a fresh deal with the Tory leader, David Cameron, than most of his senior colleagues. However, he has always insisted that policy and seat numbers, not personal preference, would decide what the Lib Dems would do in the event of no party having overall control.

A spokesman for Clegg said the Lib Dem leader was confident of retaining his seat, and that he was already working hard to defend it. “Obviously it is going to be a more defensive campaign than it was last time, but Nick is spending at least two days a week there and will continue to do so.”

Asked about Sheffield, a Labour spokesman said: “We fight for seats in all parts of the country against all opponents.”