Simon Hughes, the Liberal Democrat left-winger, was on course last night to become the party's deputy leader.
The former party president is understood to have secured the backing of more than half of its 57 MPs. Although he voted in favour of forming a power-sharing deal with the Conservatives, he is likely to prove a thorn in Nick Clegg's side.
Following the close of nominations, he will be standing against Tim Farron, the MP for Westmorland and Lonsdale, who is thought to have the support of some 15 MPs.
Mr Hughes, 59, will be the overwhelming favourite to win the position in next week's run-off. The MP for North Southwark and Bermondsey is likely to be cast in the role of a "watchdog" who will ensure that Liberal Democrat priorities are reflected in coalition policies. One ally said he wanted be an "independent but supportive voice of the party".
As one of its longest-serving MPs – he has been in the Commons since 1983 – Mr Hughes will be stressing his experience and high media profile. Many of the party's senior figures, including Vince Cable, Sarah Teather, Alan Beith, Steve Webb and Ed Davey, nominated him.
He said he was delighted by the level of his support and added: "The months ahead are a huge opportunity for our party. We must make sure that the skills and ability of every single Liberal Democrat MP is used to the full."
Like his rival, the little-known Mr Farron is on the left of the party. He said: "Now the Liberal Democrats form part of the coalition Government, the role of the deputy leader will change, but it will also be extremely important as a voice that is unashamedly partisan but unflinchingly loyal. It is vital the independence, radicalism and distinctiveness of the Liberal Democrats are maintained."
Mr Farron, a 40-year-old former higher-education lecturer, arrived in the Commons five years ago after capturing his seat from the Tories by just 267 votes. He increased his majority to more than 12,000 last month.
His supporters include Sir Menzies Campbell, the former party leader, and Chris Huhne, the Energy and Climate Change Secretary.
Mr Huhne said: "Tim Farron has the passion, experience and energy to be highly effective as deputy leader."
The contest follows Dr Cable's announcement that he is stepping down after four years as deputy leader to concentrate on his job as Business Secretary. A poll by LibDemVoice.org this week found that 60 per cent of activists wanted Mr Hughes to become deputy leader.