THE rules of engagement for armed police are under renewed scrutiny today, after it emerged that the officer involved in the shooting of a suspected terrorist told independent investigators that it was an accident.

The armed officer who led the raid on a suspected chemical bomb factory in East London said that he did not deliberately fire the shot that injured Abul Kahar Kalam, but that his gun went off during a struggle on a staircase.

His evidence is at odds with that of Mr Kahar, 23, who said that there was no tussle and the officer from the SO19 firearms unit did not issue a warning before he was hit as he emerged unarmed from his bedroom, dressed in pyjamas. Mr Kahar was transferred yesterday under armed guard from hospital to Paddington Green high-security police station to begin questioning about his alleged role in building a cyanide bomb, which security chiefs are convinced is hidden in London.

His brother, Abul Koyair Kalam, 20, told his lawyer that he denies strenously reports that he was responsible for the lone shot being fired after grappling with the police during the 4am raid.

The police emphasised that this was an MI5-led operation. They were concerned that the intelligence services appeared to be relying on a single informant. They have until Wednesday to question the brothers without special permission from a magistrate.

Sir Ian Blair, the beleaguered Metropolitan Police Commissioner, is under pressure to give a public assurance on the tactics used by his armed officers. Crown prosecutors are expected to decide by the end of the month whether to bring charges against his officers over the killing of Jean Charles de Menezes, the Brazilian who was mistakenly shot as a terrorist on July 22 last year.

It is understood that investigators from the Independent Police Complaints Commission were told that there was a struggle in the darkness during last Friday’s raid and that the Heckler & Koch sub-machinegun went off and the bullet lodged in the ceiling. A Scotland Yard source told The Times: “The officer is insistent he did not pull the trigger.”

The safety catch was off and the officer was wearing gloves and a bulky chemical and biological protection suit after intelligence warnings that there could be lethal materials hidden inside the terraced house in Lansdown Road, Forest Gate. Senior officers emphasise that weapons teams are given extensive training on handling guns while wearing the suits. Scotland Yard sources deny that the experienced officer panicked in the darkness when a figure appeared, running towards him on the stairs.

Julian Young, the lawyer for Mr Koyair, said after talking to his client: “My client is angry about these reports. He accepts he may have shouted but he says he did not struggle and did not cause his brother to be shot.”

Kate Roxburgh, who represents the wounded suspect, said that Mr Kahar was adamant that claims that he was shot by his brother were absolute nonsense. Ms Roxburgh added: “He is absolutely horrified and completely bewildered about how the police have come to this. He has had no involvement in this whatsoever.”

It emerged last night that the focus of the police search, expected to continue for most of this week, is the basement of the house, which the two brothers had converted into a gymnasium.

The lawyers for the two brothers are demanding to know why 250 officers raided their home. Both men deny any involvement in terrorism. Mr Koyair told his lawyer: “I am angry this happened to me but pleased police are doing their job.”

Senior police officers defended the decision to stage the raid. One source close to the counter-terrorist operation said: “What do we do? Ignore this bit of intelligence and risk a device going off somewhere? How do you not act on information like that? What would happen if later say we ignored that intelligence and 200 people died?”

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