Mr Hancock has always denied any wrongdoing A Lib Dem MP will not face charges over claims of “inappropriate behaviour” towards a female constituent.
Portsmouth South MP Mike Hancock, 64, was arrested on suspicion of indecent assault in October and bailed.
The Crown Prosecution Service (CPS) said the allegations centred on a series of visits the MP made to the woman’s home between March and June.
A spokesperson said there was insufficient evidence to prosecute. The MP has always denied any wrongdoing.
The CPS said it received a file of evidence from police on 8 December.
A spokesperson said: “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 account of the nature of the visits.
“We have written to the complainant to explain our decision and offered her a meeting.”
Mr Hancock said he offered help and support to the woman.
The MP’s parliamentary aide was arrested earlier in the month in a separate matter over claims she is a Russian spy.
Katia Zatuliveter, 25, who worked for Mr Hancock, was arrested on 2 December.
In an e-mail sent to the BBC from the immigration centre where she is being held, Ms Zatuliveter vowed to fight any deportation case.
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