PlayHome Secretary Jacqui Smith has attacked London Mayor Boris Johnson for ousting the UK's top police officer.
Metropolitan Police Commissioner Sir Ian Blair said he could not continue without the support of the Mayor.
Sir Ian said Mr Johnson wasted no time in using a meeting on his first day in power as Police Authority chairman on Wednesday to oust him.
But Mr Johnson branded claims of a Tory plot to oust Sir Ian as "absolutely outlandish" and said he withdrew support to improve policing in the capital.
He insisted no constitutional precedent was set by apparently undermining the prerogative of the Home Secretary to appoint the head of Scotland Yard.
Mr Johnson said he made the decision in the interests of Londoners after "widespread consultations".
He said: "I think some of the analysis I have read this morning has been absolutely outlandish. There is not and has not been any kind of party political plot by the agents of the Tories, Labour and Lib Dems. There is no party political element to this.
"I simply thought after long reflection and widespread consultation that it was a good opportunity for someone else to offer new leadership, stability and increased operational effectiveness, let me put it like that, increased operational effectiveness for the Metropolitan Police and that was not an opportunity that I could let go by."
Earlier, Ms Smith said deputy commissioner Sir Paul Stephenson would 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 which his leadership at the Met has overseen, and his continuing efforts to tackle gun, gang and knife crime.
"Sir Ian can be proud of his contribution locally and nationally."
There has been constant speculation since Mr Johnson's election in May that Sir Ian's days in power were numbered.
Sir Ian has been dogged by controversy - the most recent claims involving contracts awarded to a close friend and a race row among senior officers.
The senior officer admitted the 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.
And the hunt for a replacement for Sir Ian is on, with Sir Hugh Orde as frontrunner.
Sir Hugh joined the police force in 1977 and rose to rank of Chief Constable of the Police Service of Northern Ireland (PSNI) in September 2002.
He was involved in the inquiry into the murder of Stephen Lawrence and also played a major role in the investigation by former Met Commissioner Sir John Stevens into allegations of state collusion in a number of sectarian murders in Northern Ireland during the Troubles.
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