MP Mike Hancock will not face charges over allegations he sexually assaulted a female constituent, Hampshire Police said today.
Liberal Democrat Mr Hancock, 64, who represents Portsmouth South, was arrested over the allegations in October.
In a statement, the force said: "Hampshire Constabulary can confirm that following consultation with the Crown Prosecution Service (CPS), no further action is to be taken against MP Mike Hancock in relation to allegations of sexual assault.
"The decision from the CPS was that there was insufficient evidence upon which to charge Mr Hancock.
"The alleged victim has been notified by Hampshire Constabulary of this decision, as has Mr Hancock."
Detective Chief Inspector Paul Barton from Hampshire Police said: "Information regarding the welfare of a female from the Portsmouth area was passed to us by a third party on August 5 this year.
"Contact with the alleged victim was subsequently made and officers carried out a full and thorough investigation into the circumstances and submitted a file to the CPS."
A CPS spokesman said: "The CPS received a file of evidence from the Hampshire Constabulary on December 8 concerning allegations of sexual assault involving Michael Hancock MP and a constituent.
"The allegations centred on a series of visits to the home of the constituent by Mr Hancock between March and June 2010. Mr Hancock has stated these visits were made in his role as an MP and not for any personal purpose.
"After thoroughly reviewing the file, we have concluded there is insufficient evidence for a realistic prospect of conviction as there is no evidence to disprove Mr Hancock's account of the nature of the visits.
"We have written to the complainant to explain our decision and offered her a meeting."
Mr Hancock's parliamentary aide Katia Zatuliveter, 25, was arrested earlier this month in a separate matter over claims she is a Russian spy.
The aide, who worked for Mr Hancock for three years, was arrested on December 2 and faces deportation.
She is thought to have had access to classified defence documents as Mr Hancock is a member of the Commons defence select committee.
Ms Zatuliveter has denied any wrongdoing and has said she will fight any deportation case.
In a statement Mr Hancock said: "I have always maintained my innocence over this. I have co-operated fully with police at all times and at all times vigorously contested these allegations.
"They have now been fully investigated and I am obviously pleased that the CPS and police have concluded that there is absolutely no case for me to answer over them and are dropping any further action.
"I hope that this will draw a line under this for all concerned."