London Mayor Boris Johnson threatened to publicly undermine Sir Ian Blair if he refused to step down as head of the Metropolitan Police, a Government minister claimed.
The accusation came amid continued political wrangling over the appointment of Sir Ian's successor.
Home Secretary Jacqui Smith rebuffed the mayor's entreaties for more involvement in the selection process, by rejecting his suggestion that the two of them form the final stage interview panel.
In a letter she also ruled out delaying the appointment as the mayor suggested, saying it was important London was not without a Commissioner "for any longer than is necessary".
A member of her ministerial team, Home Office minister Lord West of Spithead, told the House of Lords the mayor had threatened to undermine the Commissioner by publicly declaring he had no confidence in him.
He said: "As I understand it, the mayor said to the Commissioner 'If you don't go I will find someone to ask me a question, with the media there, as to whether I have confidence in you and if they do I will say I haven't.'"
Barely a week after Sir Ian's resignation, the row over his departure and the process of appointing his successor shows no sign of abating.
Mr Johnson said in a letter: "You might...share my view that at this most senior level of appointment the best result is achieved by a short, tight and pragmatic set of interviews, conducted by you and me alone at the shortlisting and final interview stage."
He urged her to consider a "fairly lengthy consolidation period" before appointing a permanent replacement and argued against "moving too quickly".
But in reply, Ms Smith said she would conduct final interviews, after candidates had been shortlisted and considered by a panel including MPA members, while only having "regard" for Mr Johnson's views. She also said the new Commissioner should be a UK citizen - ruling out the possibility that Los Angeles police chief Bill Bratton might be a candidate for the role.
