Liberal Democrat MP Mike Hancock has been arrested on suspicion of indecent assault following allegations of improper behaviour towards a female constituent.
In a statement on his website, the 64-year-old Portsmouth South MP said he went voluntarily to a police station on Tuesday night and "co-operated fully" with inquiries.
He was released on police bail without charge until January 10.
A Hampshire Police spokesman said: "A man has been arrested on suspicion of indecent assault following a complaint from a woman in Portsmouth. The 64-year-old man from the Fareham area was arrested at 10am on Tuesday.
"He was questioned by police following an allegation made on Friday September 24 and has been bailed until January 10, 2011."
Mr Hancock declined to comment on the details of the case, but has previously denied any wrongdoing and insisted he only offered "help and support" to the 36-year-old woman.
Hampshire Police's involvement came as Parliamentary Standards Commissioner John Lyon was also reported to have received a complaint about the MP's behaviour.
Mr Hancock said: "I can confirm that I was questioned on Tuesday October 12 by officers of the Hampshire Police in relation to allegations made against me by one individual.
"I attended the police station voluntarily, co-operated fully and answered all questions that were asked. Normal processes now have to be followed by the police, which I entirely understand."