Metropolitan Police Commissioner Sir Ian Blair has again refused to resign over the shooting of innocent Brazilian Jean Charles de Menezes.
He has been under pressure to step down since the force was convicted last week in a trial linked to the 2005 killing.
Sir Ian, who has been criticised in a police watchdog report, said he would stay in the post and that the Met had made much progress since the shooting.
But Mr de Menezes's family said Sir Ian's position was now "untenable".
Sir Ian was commenting after a report by the Independent Police Complaints Commission (IPCC) criticised his role in the shooting.
Mayor Ken Livingstone welcomed a recommendation that no disciplinary action should be taken against two senior officers - the then Commander Cressida Dick and Assistant Commissioner Andy Hayman.
The recommendation was made by the Metropolitan Police Authority to the IPCC.
Mr Livingstone called for an end to what he called a "political witch hunt" targeting the officers and Sir Ian.
He said: "... It is outrageous that senior police officers... due to a political witch hunt, are wasting their time considering whether they will face disciplinary charges rather than being able to concentrate on carrying out their job of safeguarding Londoners."
On Wednesday, members of the London Assembly passed a vote of no confidence in Sir Ian.
And both the Conservative Party and the Liberal Democrats have called for his resignation.
Home Secretary Jacqui Smith released a statement re-stating her "full confidence" in Sir Ian in the light of the IPCC report.
The Commissioner said he had "deep and very personal regret" for the death of Mr de Menezes.
He said: "Hardly a day goes by when I have not thought about how things could have been done differently and thus Mr de Menezes would still have been alive."
But he added: "In so far as I have had sight of the report for over 18 months and have been well aware of its contents, its publication today makes no difference to the position I made clear yesterday - I intend to remain in this post.
Mr De Menezes's family said Sir Ian's position was 'untenable'
"My reasoning is very simple - by the very nature of its task, the history of the Metropolitan Police Service is littered with controversial events.
"I don't need to repeat a litany of them now but every Commissioner has such events on his watch."
Commenting on the IPCC report's criticism of the shooting he admitted that "some mistakes or miscommunications by different individuals led to a disastrous result."
He added: "I am satisfied that the MPS has made major progress in the areas recommended for review by the IPCC, particularly around armed operations, communication, surveillance and Operation Kratos, the policy for dealing with deadly and determined attackers."
But one of Mr de Menezes's cousins, Vivian Figueiredo, said: "On the issue of Ian Blair, we maintain that his position is untenable but we also believe that, whether he goes or not, will not mean that justice for Jean's death will have been achieved.
"Until all those directly involved in Jean's death have been held accountable in a court of law we will not rest."