Oaten enters leadership race suggesting that rival Campbell is too old for the job

Sir Menzies Campbell has dismissed a suggestion by his rival for the Liberal Democrat party leadership, Mark Oaten, that he is too old for the job. Mr Oaten, 41, the party's home affairs spokesman, made his barely coded criticism of 64-year-old Sir Menzies - who would be expected to stand down soon after the next general election - by saying that the Liberal Democrats required more than "interim measures" and needed "a leader with the courage of their convictions and the energy to revitalise liberalism for the 21st century".

Sir Menzies, a former Olympic sprinter, has recovered from cancer and insists he is fit to lead the party. One supporter of Mr Oaten said: "Ming has not been a well man. Leading the third party is an enormous strain. You don't have the back-up that the two main parties enjoy."

Sir Menzies admitted age would be an issue in the election but insisted: "It's not a question of how many years you've been around, but how vigorous you are and how open-minded you are. I put myself forward because I believe I have the qualities necessary, but there will be other candidates and the membership have the responsibility of deciding who they think is best able to take the party forward."

A three-horse race is in prospect. Simon Hughes, the party's president, will announce tomorrow whether he will stand.

Allies are confident that he has the backing of more than the seven MPs needed to secure him a place in the ballot of the party's 75,000 members.

Mr Oaten, who confirmed he would run yesterday, has not yet won the public support of seven MPs but enjoys the private backing of the ousted leader Charles Kennedy - some of whose allies are furious with Sir Menzies for not rallying behind him as he tried to keep his job. Mr Oaten denied that he was seeking to "avenge" the coup against Mr Kennedy.

The party's frontbench team agreed yesterday to seek to move on without recriminations and Sir Menzies and Mr Oaten promised each other they would keep the contest clean. Despite that, Sir Menzies' supporters privately described Mr Oaten as a man of "unlimited ambition, limited talent".

Lynne Featherstone, MP for Hornsey and Wood Green, has asked the candidates what part they played in the ousting of Mr Kennedy. "There are two angles running - Ming the Merciless and the plot, which I can't believe, or if he was [merciless], that there weren't such extraordinary reasons for him to be so. I need to hear him tell me that," she said.

Insisting his hands were clean, Sir Menzies insisted: "I'm satisfied that I fulfilled my responsibility to the party in this matter."

Michael Brown, a businessman who gave the Liberal Democrats £2.4m before last May's election, said he was "99.99 per cent" certain the party would receive no more of his money following its "despicable" treatment of Mr Kennedy, who was forced out on Saturday after admitting he had been treated for alcoholism.

Mr Oaten, launching his campaign outside a Westminster hotel, declared: "It is now time in the 21st century for the liberal party to modernise to get into power again. I believe I am a 21st-century liberal and I am determined to lead a 21st-century liberal party. It's about vision, energy and ambition. We have got to get across to the country that this party wants to get into power. I believe there is a hunger out there for something different in politics. I believe this party can deliver that. We need to get that message across. I have the energy and enthusiasm to do that."

He said he had attacked the "nanny state" Labour Party through his opposition to anti-terror laws and promised to expose the "fake liberals" of David Cameron's Conservative Party."

Mr Oaten failed to name any MPs backing him beyond his campaign manager, Lembit Opik, who said: "I would not be standing here telling you we are running a campaign if we were not confident we could fulfil the criteria for the election. We are confident we are players and one of the two candidates in this election."

Mr Opik said Mr Oaten had spoken to Sir Menzies and insisted the two camps would fight a positive campaign and not rake up disquiet over events leading to Mr Kennedy's departure.

Sir Menzies said the frontbench team had unanimously agreed to work towards "restoring a sense of unity and purpose" following Mr Kennedy's resignation. He also met staff at the party's London headquarters in his role as acting leader, and said they wanted to focus on the May local elections.