Commander Ali Dizaei denies the allegation
One of the country's most senior police officers is being investigated by the Metropolitan Police Authority (MPA) over alleged misconduct.
Metropolitan Police Commander Ali Dizaei is being investigated after he allegedly advised a defence team in a Met prosecution, the BBC understands.
It is alleged Mr Dizaei helped the team defending a woman accused of leaving the scene of a fatal hit-and-run.
Mr Dizaei has denied any wrongdoing. The MPA confirmed it was investigating.
"Commander Dizaei is currently being investigated by the MPA for a matter of alleged misconduct," an MPA spokesman said.
"The MPA has a statutory duty to investigate all allegations of misconduct and takes this responsibility very seriously."
West Midlands Deputy Chief Constable Phil Gormley has been appointed as investigating officer, the BBC understands.
Mr Dizaei told BBC correspondent Danny Shaw that he had not given the defendant any advice directly or indirectly, and could not recall having met her.
The Metropolitan Police did not comment.
Mr Dizaei is the president of the National Black Police Association (NBPA), which has accused the Met of "attacking black officers" after Assistant Commissioner Tarique Ghaffur was temporarily relieved of his duties.
He was at the centre of a four-year £4m investigation over allegations of perverting the course of justice and misconduct in public office.
He was cleared of all charges by the Old Bailey in 2003.