Disgruntled officers have sought to undermine Metropolitan Police chief Sir Ian Blair, Ken Livingstone has said.
Mr Livingstone said the 'radical' Met chief had his full backing
He said those passed over for promotion had done "their bit to stab Sir Ian in the back" following the shooting of Brazilian Jean Charles de Menezes.
Sir Ian was "radical and reforming" and the "best news that London police has got", London's mayor told the BBC.
But he said Sir Ian "has many enemies...who really don't want to see" the changes he is making to the force.
Mr Livingstone said if Sir Ian decided to quit over the mistaken shooting of the Brazilian, he would "lock him in the room" until he dissuaded him.
"Here is a radical and reforming commissioner who is making major changes in the police, he has many enemies in there who really don't want to see these changes, who want to hold on to the old ways... and I am sure many of them are taking every chance here to undermine him," Mr Livingstone told BBC Radio 4's Today programme.
"In the subsequent weeks we have seen clearly individuals who are disgruntled who may have been passed over for promotion doing their bit to stab Sir Ian in the back."
On Tuesday Brazilian officials said they did not believe there was a Scotland Yard cover-up over the shooting of Jean Charles de Menezes. But ambassador Manoel Gomes Pereira said he had been "perplexed" by leaks from the inquiry that contradicted early police and eyewitness reports.
Officials from Brazil are holding talks with the Independent Police Complaints Commission on Wednesday.
Earlier this week Prime Minister Tony Blair said Sir Ian had his full backing.
Mr Menezes' family want Sir Ian to resign for wrongly linking the shooting to the attempted bombings early on.
Sir Ian has said it was 24 hours before he learned the Brazilian was wrongly shot dead.
The family's lawyer expressed "incredulity" that he made statements without knowing facts.
Mr Menezes, a Brazilian electrician, was shot by police at Stockwell tube station on 22 July - the day after several failed bomb attempts - when he was mistaken for one of the bombing suspects.
Later the same day Sir Ian said the shooting was "directly linked to the ongoing and expanding anti-terrorist operation".
Mr Menezes' family have called for Sir Ian to resign
Leaked documents from the police investigation into the death appeared to contradict initial police and witness statements about the incident.
Scotland Yard was quoted as saying that Mr Menezes' "clothing and demeanour" added to suspicions that he was a suspected suicide bomber.
However, the leaked documents and photographs show the body of Mr Menezes, on the Tube where he was shot dead by police, wearing a denim jacket - not a bulky one as previously described.
In an interview on Radio 4's Talking Politics show on at the weekend Saturday Sir Ian said the shooting had to be put into context.
"Tragic as the death of Mr Menezes is, and we have apologised for it and we take responsibility for it, it is one death out of 57."