Essex Police have opened an investigation into MP Julian Knight after Scotland Yard referred an allegation of serious sexual assault.
The Metropolitan Police had previously shelved its investigation into the Solihull MP, who was stripped of the Conservative whip, and it is not clear why the case was referred onwards.
The Tories refused to restore the whip to Mr Knight after the Met dropped the case, with the party saying at the time that it had received “further complaints”.
On Tuesday, a statement from Essex Police said: “We have agreed to take on an investigation which has been referred to us from the Metropolitan Police Service.
“We are investigating an allegation of serious sexual assault.
“Detectives who specialise in cases of this kind will gather evidence and conduct a thorough investigation.”
Detective Chief Superintendent Andy Waldie will oversee the work carried out by a senior investigating officer with “extensive experience”.
“In the interests of justice and of all concerned, we have asked media outlets and others not to enter into any speculative comment or reporting on this matter,” Essex added.
“We would also remind everyone that victims of sexual offences are entitled to life-long anonymity, regardless of how a case proceeds.
“The Essex Police investigation remains at an early stage.”
Mr Knight is currently sitting in the Commons as an independent and has announced that he will stand down at the next election.
In December, the then chairman of the Commons Digital, Culture, Media and Sport Committee insisted he is “entirely innocent of any wrongdoing whatsoever” after the Met opened its investigation.
The force said in March that it was “no longer proceeding with an investigation”, with no arrests having been made.
Mr Knight urged the Tories to hand back the whip, meaning that he could rejoin colleagues in the parliamentary party.
But the Conservatives refused his demand and said that “further complaints” had been made to the Whips’ Office.
“These complaints, if appropriate, will be referred to the relevant police force, or appropriate bodies,” a spokeswoman for Chief Whip Simon Hart said at the time.
The Conservatives declined to comment on Tuesday.