Mr Oaten's sudden resignation yesterday as Liberal Democrat Home Affairs Spokesman was not only a shock to those who know him but could not come at a worse time for the Liberal Democrats.
The party is still trying to recover from the resignation of Charles Kennedy as leader two weeks ago after he confessed in front of the television cameras, that he was fighting alcoholism. His decision to quit exacerbated a damaging split in the party and provoked an acrimonious dispute in which Mr Oaten was indirectly involved between those who had called on Mr Kennedy to go and those who wanted him to stay.
But unlike Mr Kennedy's alcohol problems, which have been the subject of Westminster gossip for years, the Oaten scandal has come out of the blue and shocked colleagues and friends.
Last night friends of Mr Oaten, a popular figure at Westminster who is married with two young daughters, expressed their bemusement at the news that he had paid for sex, on several occasions, with a male prostitute at a squalid south London flat.
Mr Oaten's election agent Edward Lord said he had been "shocked" by the disclosures. "From what I know of Mark, I think this was an aberration," he said.
But as he was confronted with sordid details of his sessions with a male prostitute yesterday Mr Oaten realised his career as home affairs spokesman was over. As News of the World journalists arrived outside his detached house in the village of Bramdean, Hampshire, he asked for time to " speak to his family first". Then, early Saturday evening, he announced he was abandoning his role as Home Affairs spokesman, which had allowed him to build a platform as a high-profile opponent of the government on ID cards and anti-terror laws.
The newspaper alleged that between the summer of 2004 and February 2005 the MP visited a slightly built prostitute for sex. He is alleged to have contacted him through a gay website and paid him £80 an hour. On one occasion he had three-in-a-bed sex.
The liaison is all the more surprising since, in his role as Home Affairs spokesman, Mr Oaten has been vocal in his condemnation of a judge who received a £1m pay off package after hiring rent boys for sex. In 2004, according to The People newspaper, he condemned the decision to allow the Crown Court Recorder Roger Davies to leave his job with a huge pay-off before an investigation into his behaviour was carried out. Mr Oaten said this was "a whitewash" and a "cover-up."
Only last week, although embroiled in the Liberal Democrat leadership contest, Mr Oaten issued a statement on prostitution calling for liberalising reforms that would enable prostitutes to operate in safety and regular health checks while not tolerating the practice.
The news that his knowledge of the subject was first-hand came as a considerable shock to colleagues. In the past few days at Westminster, and even after his withdrawal from the leadership contest, Oaten has seemed his normal bouncy and jovial self. Earlier this week, as he chatted over lunch and a few glasses of Chardonnay at a restaurant in Westminster, the Liberal Democrat's spokesman on Home Affairs showed no sign that he knew of the gathering personal storm. Neither did anyone else in politics seem to be aware he had been leading a double life.
At lunch, the main topics of conversation included how hard Mr Oaten found it spending time away from his wife and two young daughters, Alice and Milly, while he worked on the leadership contest. There was no hint of his alternative lifestyle as he talked about his wife Belinda, who used to import clogs, and who only days earlier had smiled for the cameras as he launched his leadership bid.
The MP for Winchester also joked how his baldness was a potential stumbling block to success and that Sian Lloyd, the weather presenter and fiancee of Mr Oaten's supporter Lembit Opik, had volunteered to improve his tie collection with a shopping trip to Selfridges. Despite appearing upbeat about his chances to win the leadership race, only a day later the news broke that Mr Oaten was pulling out of the contest.
A popular figure, the 41-year-old MP had said the Lib Dems should be prepared to talk to either of the other main parties in the event of a hung Parliament. But he said it needed challenge the "nanny state" instincts of the Labour Party and take on the "fake" liberalism of Conservative leader David Cameron.
Born in Watford in 1964, Mr Oaten attended a local comprehensive and went on to study as what was then Hertfordshire Polytechnic. Between 1988 and 1992, he worked as a consultant for lobbyists, Shandwick Public Affairs. In 1997, he caused a huge parliamentary upset after he won by only two votes the Winchester seat, but the contest was declared invalid. Instead he was forced to fight a by-election in November but humiliated the Tories by winning with a margin of 21,556 votes. Mr Oaten has held the seat ever since and went to become the Lib-Dems spokesman for disabilities as well as a member of the party's foreign affairs and defence team.
After the 2001 general election, he was voted chairman of the Parliamentary party and two years later replaced Simon Hughes as Liberal Democrat Home Affairs spokesman.
However, last night, all these achievements were overshadowed by his own admission that he had made 'errors of judgement', errors splashed over the pages of a tabloid newspaper.
FALLS FROM GRACE
DAVID MELLOR: The Chelsea-supporting Tory heritage minister had an affair with Antonia de Sancha in 1992. Newspapers claimed he slept with the actress while wearing a Chelsea shirt, but this detail was invented.
RON DAVIES: The former Welsh secretary was forced to resign after a "moment of madness" on Clapham Common in October 1998. He claimed no sexual encounter had taken place, but he later said he was bisexual.
PIERS MERCHANT: The Tory MP resigned in October 1997 after an affair with his researcher, Anna Cox, a former Soho hostess. The friendship had been exposed earlier that year.Reuse content