SIR MENZIES CAMPBELL was fighting to restore the credibility of the Liberal Democrats last night after Mark Oaten, the former leadership hopeful, resigned over revelations of an affair with a male prostitute.

Mr Oaten, 41, who is married with two children, quit as the party’s home affairs spokesman when his clandestine encounters were exposed by the News of the World. The revelations came two weeks after Charles Kennedy resigned as leader because of his battle with alcoholism.

Supporters of Sir Menzies lost no time in suggesting that the latest high-profile Lib Dem disaster added to the acting leader’s case to fill the permanent vacancy.

Jeremy Browne, MP for Taunton, said: “There are times when political parties collectively come to the view that they want to be adventurous and take a chance and there are times when parties hanker after a bit of stability and credibility. Menzies Campbell provides the authority, credibility and stability the party needs.”

His words may be seen as an attack on Chris Huhne, the recently elected MP for Eastleigh, who is seen as a dark horse in the leadership battle.

Sir Menzies insisted yesterday that the party would not be deflected by the latest controversy. “The task is to draw the party together and move forward,” he told Sky News. “No party is entirely subject to what happens to any one individual. The party is much bigger than that. My task as acting leader is to secure a sense of unity and purpose. We have a strong political agenda. We have a sense of purpose, we have great deal to do and a great opportunity in which to do it.”

The News of the World reported that Mr Oaten first contacted the unnamed prostitute, who was then aged 23, in 2004 through a gay website and they met regularly over a six-month period. On one occasion a second male prostitute was said to have been involved. The man told the paper: “Oaten was a regular punter for six months . . . He’s a very troubled man living a very dangerous double life.”

Mr Oaten, who was reported last night to be trying to save his 13-year marriage, said in a statement: “I would like to apologise for errors of judgment in personal behaviour and for the embarrassment caused, firstly to my family but also to my friends, my constituents and my party. I will not be commenting further at this time and would now ask for some space and personal privacy for me and my family.”

As home affairs spokesman, Mr Oaten enjoyed a high profile recently, taking a leading role in the battle over the Government’s controversial anti-terrorism legislation.

He sought to underline his credentials as a family man, inviting the cameras into his home on the eve of his leadership bid to film him sitting down for a meal with his wife and children.

A party spokesman said that Mr Oaten’s deputy, Alistair Carmichael, would temporarily assume overall responsibility for home affairs.

Mr Oaten pulled out of the race to succeed Mr Kennedy on Thursday, citing a lack of support among MPs. Lembit Opik was the only MP to say that he was backing him.

Lib Dem opinion poll ratings have plummeted since Mr Kennedy’s resignation and the latest disclosures are unlikely to improve them. To cap a dreadful week for the party, Lord McNally, the Lib Dem leader in the House of Lords, admitted that he, too, had been an alcoholic in the 1980s.

Mr Huhne said that Mr Oaten’s resignation was a regrettable loss. “I think if you are in public life and you are an MP and you take a high-profile role, then I’m afraid you are going to be subject to scrutiny,” he told the Sunday AM programme on BBC One.

Mr Oaten’s election agent, Edward Lord, said that he had been shocked by the disclosures. “From what I know of Mark, I think this was an aberration,” he told Sky News. “We are a liberal party and for the party and its members, Mark’s private life was just that. It simply was not an issue. His performance, I don’t think, was ever affected.”

Alistair Carmichael, 40, Mr Oaten’s successor as home affairs spokesman, will be seen as a safe pair of hands for the post. First elected in Orkney and Shetland in 2001, he is Charles Kennedy’s neighbouring MP but one of those most outspoken about the need for the former leader to step down.

He is popular with colleagues and won respect for his grasp of detail while representing the party on the committee stages of the identity card and terror Bills. Mr Carmichael lives on Orkney with his wife, Kate, a vet, and their two children.

After Mr Oaten’s downfall three remaining Liberal Democrat leadership challengers are unlikely to vie for the support of Mr Opik. Mr Opik, who stood by Mr Kennedy as party leader right up to the last minute, switched to Mr Oaten and was by the Winchester MP’s side when he quit the contest.

Privately, Lib Dems are whispering that none of the candidates — Sir Menzies, Simon Hughes and Mr Huhne — would want the endorsement of the MP for Montgomeryshire. “The last thing anyone wants is for Lembit to declare for them,” said one party source. “They’re calling it the Curse of Lemsip.”

Mr Opik, 40, is not renowned for his luck. He is a keen astronomer and has often warned about the dangers of an asteroid colliding with Earth and wiping out the human race. He is engaged to Sian Lloyd, the ITV weather presenter, and the couple’s wedding is due to take place this year.

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