Sir Menzies Campell said today that the public could still trust the Liberal Democrats after Mark Oaten, a former leadership hopeful, resigned over an affair with a male prostitute.

Mr Oaten, 41, who is married with two children, resigned 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.

Lib Dem opinion poll ratings have plummeted since Mr Kennedy quit 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.

But today Sir Menzies, speaking as part of his leadership campaign at the Eden Project in Cornwall, reassured the public that they could still trust the party.

He said: "Look at the quality of the Liberal Democrat MPs in Cornwall, how they fight for their constituents. That commitment I want to see the party demonstrate throughout the UK."

Supporters of Sir Menzies hinted 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 - whose constituency Sir Menzies is due to visit this afternoon - 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 stressed that he would bring "experience and maturity" to the Liberal Democrats. "I want to create a sense of unity and show a sense of professionalism," he said. "We had our best election result in 2005 and we have a responsibility to use that to take us forward."

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."

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

The troubled MP will be asked to face his constituency party within days, after the chairman said today he wanted to discuss the allegations. Harvey Cole, the chairman of the Liberal Democrat constituency party in Winchester, said that he would be inviting Mr Oaten to a meeting with the local party’s executive.

"We want to have a discussion, clear the air and decide the best way forward and I would want to have Mark’s views by then," he said. "I do not think we are in a panic to have a meeting immediately. Let the dust settle a bit first."

Mr Cole said that the meeting would not be a "showdown" and that Mr Oaten was "one of the best backbench MPs in the country and, as the local MP, he has my full support".

Today the whereabouts of the former home affairs spokesman was unknown. Many voters in the affluent Hampshire constituency were said to be finding the lurid allegations of three-in-a-bed sex acts hard to digest.

Mr Oaten has until now been very popular locally, due to his hard work in a constituency he famously took from the Conservatives in 1997 by just two votes, then held in 2001 with a majority increased to nearly 10,000. A radio phone-in on a local station today indicated some people would never vote for him again, but others were sympathetic to his plight.

Mr Cole said that, having spoken to party members, most were still supportive. "It’s difficult to generalise as we have close to 600 members but taking a cross-section, they are certainly supportive," he explained. "There are an awful lot of people with something in their closet at some stage."

Mr Cole said he had not spoken to Mr Oaten directly - only to those with him - and he would not go into the details of the politician’s state of mind second or third-hand.

At the last election, Mr Oaten was returned with his majority cut by just over 2,000. Party activists are likely to fear that voters could desert him in larger numbers.

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