Former Liberal Democrat leadership challenger Mark Oaten has stood down as the party's home affairs spokesman over an alleged affair with a rent boy.
Mr Oaten asked for "space" and "personal privacy"
Mr Oaten released a statement apologising for the "embarrassment" caused to his family, friends and the Liberal Democrat party.
Married Mr Oaten, 41 and the MP for Winchester, dropped out of the Lib Dem leadership race this week.
The statement follows claims to be made in a Sunday newspaper.
News of the World managing editor Stuart Kuttner said Mr Oaten had been confronted with details of a relationship with a 23-year-old rent boy by reporters from the Sunday paper.
In a statement Mr Oaten said: "I have stood down as home affairs spokesman for the party.
"I would like to apologise for errors of judgement 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."
Lib Dem chief whip Andrew Stunell said Mr Oaten had stood down "with immediate effect" as home affairs spokesman.
"He has apologised to his family. He has apologised to his constituents who he always served well," Mr Stunell said.
"He and his family now need to have their personal privacy respected."
Keith Gladdis, Whitehall editor of the News of the World, justified the paper's story.
He said: "Mark Oaten is an MP, an MP who has been elected on a platform of being a family man.
"He's also an MP who's a front bench spokesman - a front bench spokesman who then went on to stand as a potential leader of the Liberal Democrat party. That is someone who quite clearly has a public life."
Mr Oaten's resignation as home affairs spokesman comes only two weeks after the party's leader, Charles Kennedy, stepped down after admitting he had received treatment for a drink problem.
Mr Kennedy's resignation prompted the leadership battle.
When standing down as the Lib Dems leadership challenger on Thursday, Mr Oaten said the other contenders all "had much more support" among MPs.
His withdrawal leaves Sir Menzies Campbell, Chris Huhne and Simon Hughes as the remaining candidates.
Deputy home affairs spokesman, Alistair Carmichael, will temporarily take over the role.