Nick Clegg has invoked "disciplinary procedures" against a Liberal Democrat MP accused of sexual assault in a High Court civil action.
Mike Hancock is being sued by a "vulnerable" constituent, accusing him of sexual assault after she contacted him for help in a neighbour dispute.
Mr Hancock, who vigorously denied the claims, was arrested by police over the allegations in 2010 but no action was taken as the Crown Prosecution Service said there was insufficient evidence for a prosecution.
Last night a Lib Dem spokesman confirmed that the Deputy Prime Minister was convening "an urgent meeting under the disciplinary procedures of the parliamentary party" between himself, Mr Hancock, party deputy leader Simon Hughes MP and party chief whip Alistair Carmichael.
The statement said: "Following Mike Hancock's receipt of legal papers in a High Court civil action, Nick Clegg has asked the chief whip to convene an urgent meeting under the disciplinary procedures of the parliamentary party between Nick Clegg, Simon Hughes, the chief whip and Mike Hancock.
"Mike Hancock strenuously denies the accusations made in the civil action. We are not prejudging the outcome of the case, but given the seriousness of the allegations, Nick Clegg has instructed the chief whip to invoke the disciplinary procedures of the party."
Mr Hancock, MP for Portsmouth South, was also the subject of controversy when his Parliamentary assistant, Russian Katia Zatuliveter, was accused by the Security Service of being a spy passing information to Moscow.
However, the 26-year-old, who admitted to having an affair with the MP while he sat on the Defence Select Committee, was granted leave to remain in the UK by the Special Immigration Appeals Commission (Siac) in November 2011.