Boris Johnson branded claims of a Tory plot to oust Britain's most senior police officer as "absolutely outlandish".
The London Mayor said he withdrew support from Metropolitan Police Commissioner Sir Ian Blair 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.
Sir Ian resigned on Thursday, blaming Mr Johnson and said he was not leaving because of any failings.
Home Secretary Jacqui Smith accused the Mayor of acting without authority or respect by pushing Sir Ian out for political reasons. But speaking at City Hall, 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."
The procedure for removing the Met Commissioner is that the Metropolitan Police Authority (MPA), its board of governors, must seek the home secretary's approval.
But Sir Ian's sudden resignation at the hands of the Mayor has led to claims the role is more politically vulnerable than ever. Some claimed it is now almost inevitable that there will be a change of Commissioner with every new London administration.
All eyes will now turn to City Hall on Monday when Mr Johnson will chair his first meeting of the MPA.
