Nominations are due to close in the by-election seen as the first major test of how the Conservatives and Liberal Democrats – sharing power in Westminster – intend to campaign against each other in the country.
The contest for Oldham East and Saddleworth was triggered by a court decision annulling the general election result from May, when Lib Dem candidate Elwyn Watkins missed out on the seat by just 103 votes. It was declared void by an election court last month which found that victorious Labour candidate Phil Woolas had made false statements about Mr Watkins.
Although Mr Watkins is Labour’s nearest challenger, the constituency was a three-way marginal in May, with Conservative Kashif Ali – who is standing again – less than 2,500 votes behind.
Since then the Lib Dems’ fortunes have plummeted in national polls, suggesting any advances made by the Tories in Oldham East and Saddleworth will put paid to Mr Watkins’ hopes of winning.
David Cameron has raised eyebrows by wishing Mr Watkins well in the January 13 poll, fuelling suspicions that Tories are not planning to mount a serious challenge.
Mr Cameron stressed this week that he would be visiting the constituency to campaign in person – a rare event for a prime minister. But he went on to describe it only as a “likelihood” that the Tories and Lib Dems would campaign as separate parties at the next general election.
Asked to clarify his “likelihood” remark , the Prime Minister added: “We are separate parties, we fight elections as separate parties, that is what I fully expect to happen at the next election.”
On the by-election, he said: “I will be going and supporting the Conservative candidate but again the campaign will be a slightly more friendly one between the Conservatives and Liberal Democrats than perhaps some of the previous by-elections we have been involved in.”
Deputy Prime Minister and Liberal Democrat leader Nick Clegg visited the constituency on Wednesday, saying his party was fighting for “every single vote”.
Labour has selected Debbie Abrahams as its candidate for the by-election. Candidates from a range of smaller parties, including the British National Party and the Monster Raving Loony Party, are expected to be confirmed after the close of nominations at 4pm.