Conservative MP Andrew Bridgen has been arrested on suspicion of sexual assault and released on bail.
It is understood the 46-year-old MP for North West Leicestershire was arrested in relation to allegations of assaulting a 29-year-old woman in central London in the early hours of Thursday morning.
Mr Bridgen is a married father-of-two who entered Parliament at last year's General Election and is regarded as being on the right of the party.
Scotland Yard said in a statement: "A 46-year-old man has been arrested on suspicion of sexual assault against a 29-year-old woman at an address in SW1 in the early hours of Thursday morning. He has been bailed to return on a date in mid-July."
Police declined to confirm the identity of the arrested man. A spokesman indicated that the address in SW1 - the London postcode which includes Westminster - was not the Houses of Parliament.
A Conservative spokesman later said: "At the moment, this is a matter for the police, who are investigating, and it would be inappropriate to comment further until the facts are clear."
Mr Bridgen and wife Jacqueline were married in 2000 and have two sons, Alexander and Benjamin. After training as an officer in the Royal Marines, he worked for his family's gardening business and set up vegetable firm AB Produce with his brother in 1988.
Since winning the former Labour seat of North West Leicestershire with a majority of 7,511 in the May 2010 election, Mr Bridgen has attracted attention in the Commons as a campaigner against the Alternative Vote in the referendum on electoral reform.
At his home in Coalville, Mr Bridgen was offered support by Graham Allman, chairman of the North West Leicestershire Conservative Association.
As he left, Mr Allman told reporters that the MP is "a good family man", adding: "I have known him a long time, he is a good guy, an all-round good guy, good for the constituency - a very popular man."