The traditional principle that Britain’s police should be unarmed, and usually are, is one that all parties pay lip service to and most voters seem to support. The total Met force of 31,000 has only about 2,000 officers allowed to carry firearms (with 440 of these further trained as specialists). So the implications of the police policy as described by Stevens took some time to sink in. But the incident has raised questions about the future of British civil liberties, exposing fault lines not simply between left and right, or police and public, but within the police force itself.

The assumption on which the policy rests is that the police’s suspicions will always be justified; and at moments of crisis, this is what everyone wants to believe.

The normally scrupulous Daily Telegraph reported that “the officers had become concerned that their target was carrying a bomb not in a rucksack or holdall — he was carrying neither — but beneath the bulky, dark jacket he was wearing despite the warm weather … The man, of Asian appearance and in his 20s, walked into Stockwell Tube station and went to buy a ticket. At about 10am, a senior officer gave the order for his armed men to challenge the suspect.

“Instead of giving himself up, the man panicked, vaulted the ticket barrier and sprinted down the escalator to a platform where a train was already waiting with its carriage doors open. Several armed officers were in pursuit and, according to witnesses, the suspect stumbled as he tried to get into one of the carriages. By the time he half-ran, half-fell onto the train, three officers, at least one of them holding a low-velocity pistol, pounced on him, shooting him five times in the head.”

It was not until three weeks later that a leak of documents from the investigation into the killing established that almost every detail of this account was false. De Menezes was not “of Asian appearance” — nor, incidentally, was the man the police were really hunting, a Somali. The senior officer involved “who gave his men orders” was a woman. De Menezes did not run through the station but paused to pick up a free newspaper, and used his season ticket to pass through the turnstiles normally. He did not run until the train came in. He did not fall over until a police officer grabbed him and held his arms, immobilizing him. At this point another police officer shot him in the head — not five, but seven times. Some of these details are still contested, but a photograph of his body shows quite clearly what may be the most important fact: He was not wearing a heavy top that might have suggested or concealed a bomb, but a pale-blue denim jacket.

By the time these details emerged the four presumed suicide bombers had all been caught and arrested, without a shot’s being fired. No one seriously believes Britain has seen its last bomb, but the next ones won’t come for a while. So while the fear is over, for the moment, the leaked documents have produced a furious debate on all aspects of the police’s tactics.

Although the debate contains elements of a left-right split, it has more to with a struggle over the soul of the police force and thus of the future of Britain’s struggle against terrorism. The right-wing press carried a number of articles suggesting that it was absurd to criticize policemen who shot anyone they thought was a terrorist. The Daily Express, owned by a man who made his fortune in porn, and which has carried, since the bombings, a Union Jack and “Britain defiant” on its masthead, ran the front-page headline: “It Was Just a Tragic Mistake: Why the Police Should NEVER Face Murder Charges Over Shot Brazilian.” Murdoch’s Sun ran an eloquent column by its star columnist defending “the poor bloody infantry” and asking what would have been said had de Menezes really been a suicide bomber and not been shot.

But the most interesting reaction came from the most influential right-wing paper in the country, the Daily Mail, which has demanded the resignation of commissioner Blair, rather than the policemen who actually shot de Menezes. The Mail hates Blair, whom it considers too liberal and “politically correct.” An Oxford graduate who worries about logos and symbolism, Blair has tried to stamp out racism in the police force. The Mail, with a largely suburban readership, is prone to campaigns against London policemen: Its previous target was Brian Paddick, the most senior openly gay policeman in the capital, who was in charge of Brixton when he ordered his force to concentrate on hard drugs, not on cannabis.

All this resonates with a macho and conservative subculture within the force, and there is no doubt that some policemen have spread leaks against Blair. He has made his own position more difficult by his overconfidence and one dreadful stroke of bad luck: Interviewed on the radio on July 7, the day of the London bombings, he said that British anti-terrorist policing was the envy of the world. Within three hours of his comments, the first round of bombs had gone off and killed 53 people.

He has been attacked from the left for allowing the officers who actually shot de Menezes to go on vacation immediately after the incident. But it looks as if the government has decided to back him, partly for the reasons that the Daily Mail is trying to destroy him. He is committed to reforming the police and to making them acceptable to the communities from which they must draw their informants. These reforms, along with controlling the armed police squads, are absolutely essential for a proper anti-terrorist campaign. (Blair estimates that about a fifth of his men are opposed to his reforms.)

Most crimes are not solved, as they are in many novels, by detecting criminals from the evidence they leave. On the contrary, the police know pretty well who the serious criminals are on their patch. Their job is to find evidence that will tie known criminals to particular crimes, normally by using intelligence. This is why police need consent, or at least legitimacy, from the communities they police. If no one will talk to them, no crimes will get solved and no criminals convicted.

But it’s not just a matter of the police being trusted. The police must also be feared as more powerful than criminals; otherwise their guarantees of safety to witnesses can’t be believed. But fear on its own won’t do, which is what right-wing critics never understand. Nor do some policemen.

There have been worrying signs for some time that the members of the London police’s elite firearms branch believe they should never be punished for shooting someone they suspect to be a terrorist. Last autumn, over a hundred of them went on unofficial strike after two of their colleagues were charged with murder for shooting in the street Harry Stanley, a Scottish carpenter who had been carrying a chair leg in a plastic bag. An anonymous caller had identified him as an Irishman carrying a shotgun.

There is no offense, in British law, of being drunk while in charge of a chair leg. Even if there were, the law is clear. The police are not allowed to shoot anyone unless they honestly and reasonably believe that it is the only way to save other lives (including their own). A dogged five-year campaign by Stanley’s family, represented by the law firm of Cherie Blair, the prime minister’s wife, led to a trial for murder of the two policemen who shot him. They were acquitted after persuading the jury that they had made an honest mistake. They have now been rearrested following a further investigation: Forensic evidence suggests they shot him from behind, so he couldn’t have been brandishing the chair leg at them.

Meanwhile, an investigation has been launched into the leaks from the independent investigation into de Menezes’ death. There is still controversy over the closed-circuit TV (CCTV) footage of the tube station, which would clear up a great deal of the story. Some police sources have claimed that the cameras were empty or malfunctioning. Others, in apparent leaks from the investigative team, have said this is nonsense. The whole story may not emerge until the investigation is complete, in about six months’ time.

But whatever happens in the case of Jean Charles de Menezes, the policy of shooting without warning has been for the moment discredited and may be abandoned. It depends too much on intelligence’s being infallible, and it never is. Even high technology doesn’t seem to have helped here. Although the police had excellent CCTV images of the bombers they were hunting when they shot de Menezes, the officer whose job it was to identify suspects leaving the block of flats they were watching failed to confirm de Menezes’ identity because he was, at the crucial moment, taking a leak.