MAYOR of London Boris Johnson has been blamed for forcing Britain's most senior policeman to quit his job.

Metropolitan Police Commissioner Sir Ian Blair said Mr Johnson wasted no time in using a meeting on his first day in power as Police Authority chairman to oust him.

And Sir Ian said he could not continue without Mr Johnson's support.

Mr Johnson praised Sir Ian's lasting and distinguished service, but said the force needed fresh leadership.

Following the announcement Gordon Brown paid tribute to Sir Ian, saying that he had made a huge contribution to the safety and security of Britain.

He highlighted how Sir Ian led the response to the July 2005 terrorist attacks in London.

Home Secretary Jacqui Smith said deputy commissioner Sir Paul Stephenson will take over as acting head when Sir Ian stands down on December 1. She said: "I pay tribute to Sir Ian for the massive reductions in crime his leadership at the Met has overseen, and his continuing efforts to tackle gun, gang and knife crime."

Sir Ian has been dogged by controversy. He has admitted the ongoing inquest into the death of Jean Charles de Menezes was the force's greatest challenge since the Stephen Lawrence inquiry.

But it was the changing political landscape in London that finally finished off the one-time darling of New Labour. Former London Mayor Ken Livingston said he regretted the `political' decision. He said: "Whoever now takes the job will know they may be asked to leave at a change of election."

Announcing his resignation, Sir Ian said: "Without the mayor's backing I do not think I can continue in the job.

"The new mayor made clear, in a very pleasant and determined way, he wished there to be a change of leadership."

Mr Johnson will chair his first meeting of the Metropolitan Police Authority, the Met's board of governors, at City Hall on Monday.

He said: "There comes a time in any organisation when it becomes clear it would benefit from new leadership."