Boris Johnson was at loggerheads with the new acting head of the Metropolitan Police today after apparently pre-judging a police investigation into the conduct of a Conservative MP.

The Mayor of London, speaking in his capacity as the chair of the Metropolitan Police Authority, said he had a “hunch” that Damian Green would face no charges over after an investigation into leaks from the Home Office.

Speaking after his first public outing as acting commissioner of the Metropolitan police, Sir Paul Stephenson said it was “entirely inappropriate” to pre-empt to result of an ongoing police investigation.

“I’m quite clear that we should not pre-judge the outcome of this inquiry,” Sir Paul said.

Mr Johnson faced hostile questioning during a meeting at City Hall in which he admitted that he had spoken to Mr Green despite having discussed the investigation with senior officers in his capacity as MPA chair.

Len Duval, a former chairman of the MPA and Labour London Assembly Member, repeatedly asked the Mayor which of his private conversations with the police would be made public.

“Do you intend to use ongoing operational police information for political advantage?” he asked.

Mr Johnson replied that he would not, adding: “Perhaps I should be arrested for leaking the details of my own conversation.”

Since Mr Johnson appointed himself the chairman of the MPA he has forced the resignation of Sir Ian Blair as commissioner of the Met and now appears to be in disagreement with his temporary replacement.

After the meeting Mr Duvall called for the Mayor to consider his position as chair of the MPA.

He said: "It is astonishing that the Mayor, following a briefing from senior police officers, has been speaking to a suspect under police investigation. He received information as chair of the MPA, then went to his political ally and old friend, who is now under criminal investigation. This is not appropriate behaviour for a chair of the police authority."

Sir Paul had earlier defended the police’s handing of the investigation into alleged leaks from the Home Office by a young civil servant to Mr Green, a shadow minister.

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