London Mayor Boris Johnson faced a formal investigation tonight into his role in the Whitehall leaks inquiry.
The Tory politician is accused of prejudging the outcome of a police investigation into his close friend and colleague MP Damian Green.
Mr Johnson told a meeting of the Metropolitan Police Authority (MPA) last month he believed Mr Green would be vindicated and admitted discussing the case with him.
A sub-committee of the London Assembly's standards board is believed to have decided the matter should be investigated at a private meeting earlier today.
They referred it to officers at both the Metropolitan Police Authority and the Greater London Authority.
The original complaint came from London's Labour group leader Len Duvall, who was Mr Johnson's predecessor as MPA chairman.
Mr Duvall claimed Mr Johnson, who was speaking in his capacity as MPA chairman, is in "serious breach of the codes of conduct".
He said the Mayor should not have revealed information given to him privately by senior police officers.
Mr Duvall also said Mr Johnson should not have discussed the case with Mr Green, as he was a suspect in a criminal investigation.