Debate over the police "shoot-to-kill" policy against suspected suicide bombers has intensified after the killing of an innocent man on the Tube.
Lord Stevens believes it would be a mistake to change policy now
Officers shot dead Jean Charles de Menezes, 27, in Stockwell, London, on Friday, thinking he was a terrorist.
Lord Stevens, the former Met police chief who brought in the policy, insists the principle remains correct.
But ex-foreign secretary Robin Cook has joined Muslim leaders in calling for a review to prevent further tragedy.
Meanwhile, Ken Jones, Chief Constable of Sussex Police and chairman of the Association of Chief Police Officers' terrorism committee, denied operating a "shoot-to-kill" policy.
He said: "Everything else must be tried first before we consider taking life to save life.
"However, if we get to the point of no return as it were there's a moral duty, if not possibly a legal duty, on us as police officers who are armed and able to perhaps deflect an attack to take life to save life."
Mr Cook said the death of Mr Menezes had been a "serious blow" to relations with Brazil and police would have to look again at the policy.
He said: "They plainly will not want to have anything approaching a repeat of that and I am quite sure they will be tightening up the guidelines and the rules of engagement to make sure it doesn't happen again."
Current Met Police Commissioner Sir Ian Blair has apologised to Mr de Menezes' family and spoken of his "deep regrets", but defended the actions of his officers.
"What we have to recognise is that people are taking incredibly difficult fast time decisions in life threatening situations," he said.
Sir Ian said there was "no point" shooting a suspect in the chest as that is where a bomb would most likely be and it would detonate.
Lord Stevens told the News of the World the policy, which he described as a "shoot-to-kill-to-protect", was correct despite the chance "tragically of error".
The former Met Police Commissioner had sent teams to Israel and other countries hit by suicide bombers.
There they learned a "terrible truth" that the only way to stop a suicide bomber was to "destroy his brain instantly, utterly" to prevent a dying bomber activating a device.
Previously, officers fired at the offender's body, "usually two shots, to disable and overwhelm".
Lord Stevens said: "We are living in unique times of unique evil, at war with an enemy of unspeakable brutality, and I have no doubt that now, more than ever, the principle is right despite the chance, tragically, of error.
"And it would be a huge mistake for anyone to even consider rescinding it."
Northern Ireland Secretary Peter Hain also backed the police strategy.
He spoke of the "enormous pressure on the police who are seeking to protect all of us, and we need to be understanding about that".
However, the Muslim Association of Britain's Azzam Tamimi said: "It doesn't matter whether he (Mr Menezes) is a Muslim or not, he is a human being.
"It is human lives that are being targeted - whether by terrorists or, as in this case, by the people who are supposed to be catching the terrorists.
"I just cannot imagine how someone pinned to the ground can be a source of danger."
Sir Iqbal Sacranie, of the Muslim Council of Britain, said: "It's vital that the utmost care is taken to ensure that innocent people are not killed."
And Massoud Shadjareh, chairman of the Islamic Human Rights Commission, called for a public inquiry, adding: "You can't even put someone in prison on suspicion, how can you kill them like that?"