One of the Met's most controversial senior officers faces an inquiry into whether he leaked confidential information to the press.
The Metropolitan Police Authority (MPA), which oversees the force, said it received a complaint about Brain Paddick, a deputy assistant commissioner.
Claims by Mr Paddick has created new questions over Met chief Sir Ian Blair's handling of the police shooting of Jean Charles de Menezes.
According to the BBC, Mr Paddick alleged one of Sir Ian's private staff knew within six hours the wrong man had been shot dead at Stockwell Tube station.
The commissioner has so far insisted that he only found out about it the next day.
Yesterday the Met said the allegation against Sir Ian was "simply not true".
The private staff member "has categorically denied this," a Met spokesman said. "This has also been corroborated by other staff in the private office."
The Independent Police Complaints Commission (IPCC) is still investigating Sir Ian's handling of the shooting.
Mr Paddick, the Met's highest ranking gay officer, is no stranger to criticism. He championed a relaxed approach to cannabis possession when commander of Lambeth, south London.
Accusations that he allowed the drug to be smoked in his own home caused him to be suspended briefly. The claims were later shown to be false.
However, the MPA said the alleged leak it is investigating has "no connection whatever" with Mr Paddick's claims about when Sir Ian's staff knew of Mr De Menezes.
The MPA declined to say what information was allegedly leaked. It was making "preliminary inquiries" to decide whether there was "any matter that warrants investigation", the authority added.
Mr Paddick did not want to comment while inquiries are underway.
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