Simon Hughes today launched his bid to become deputy leader of the Liberal Democrats, with the backing of outgoing deputy and Business Secretary Vince Cable.
Launching his candidacy in his south London constituency, Mr Hughes said he already had pledges of support from 25 Lib Dem MPs - just four short of the 29 votes needed to win the June 9 ballot.
The Bermondsey and Old Southwark MP is regarded as being on the left of the party and may be viewed as a focal point for activists uneasy about the coalition with Tories, but he has been publicly supportive of the deal which brought Lib Dems into government.
Despite being a frontbench spokesman for much of his 27-year parliamentary career and holding the energy and climate change brief in the run-up to this month's election, Mr Hughes was not rewarded with a ministerial job in the Tory-Lib Dem Government.
He said today he aimed to ensure that the Liberal Democrats remain a "strong, supportive but independent voice within and around the coalition".
Mr Hughes, 59, is the second candidate to throw his hat into the ring following Mr Cable's surprise resignation as deputy leader on Wednesday. Westmorland and Lonsdale MP Tim Farron announced yesterday that he will be a candidate, with the backing of former leader Sir Menzies Campbell.
Announcing his candidacy under a slogan declaring him "the life and soul of our party", Mr Hughes said: "After campaigning for three decades for liberal democracy in Bermondsey and Old Southwark, London and around the country, it would be a great honour to serve my party as deputy leader.
"Our party is at the beginning of an exciting journey in a difficult and challenging time for our country.
"We are now in government and implementing Liberal Democrat policies for the first time in generations. The first UK coalition for 65 years will mean great changes and challenges for Liberal Democrat MPs and our party around the country.
"I believe that I have the strength and breadth of experience to make sure that our party is a strong, supportive but independent voice within and around the coalition. We must hold fast to our ambition to grow our party and expand the number and diversity of Liberal Democrat elected representatives at all levels of government in the five years ahead."
Mr Cable, a former Labour member who is also on the left of the Lib Dems, said Mr Hughes would "uphold the values of our party".
"Simon has given the most phenomenal service to the party over his 27 years as an MP. He represents the best traditions of the Liberal Democrats, both as a parliamentary campaigner and community activist," said the Business Secretary.
"Simon is the person best placed to follow me as deputy leader and uphold the values of our party."
Mr Hughes, who entered Parliament in a 1983 by-election and served as Lib Dem president from 2004-08, has twice stood for the Lib Dem leadership but lost on both occasions - to Charles Kennedy in 1999 and to Sir Menzies in 2006.
MPs with the required backing of five colleagues by the time the parliamentary party meets next Wednesday will go forward to a ballot of the 57 Lib Dem MPs on June 9.
Mr Hughes's low key launch took place at the Salmon youth centre in Bermondsey with an audience which included children from a local primary school.
He said Lib Dem leader Nick Clegg had his full support and part of his own role if elected would be to show the public that the party had not "sold out".
He said: "The challenge for us as a party is to be seen to be different from the Tory Party but also to make sure that we take on successfully the Labour Party."
He described the coalition as "the most fantastic opportunity" for the party, adding: "Of course there are risks. We could have stepped away, we could have said a Tory minority government can run the country but that would have been shirking our responsibility."
He said although it would be "fantastic" to be a minister in the coalition his own skills and experience meant he was best equipped to "make sure the party feels represented in Parliament".
Asked about a role as deputy leader, he said: "It's about making sure the public keeps on hearing where there are differences and knows that we haven't sold out."
He said the party voice must continue to be heard on issues such as nuclear weapons and the environment.
Mr Hughes added he would expect a "fair minded" Speaker in the Commons to come to the Lib Dem deputy leader third, after the Tories and the Labour Party.
He said: "It would be a nonsense if nearly seven million people didn't see and hear our point of view on a regular basis."