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The New York Police Department on Thursday admitted making a mistake in publishing information coming from the Metropolitan police’s terrorism investigation which suggested mobile phone alarms were used to detonate the July 7 bombs.

Scotland Yard detectives said they were close to identifying the precise explosive mix used by the bombers after almost a month of painstaking forensic analysis. But it played down the NYPD’s comments on mobile phones, insisting such a conclusion was still “well ahead of where the investigation is at the moment”. It has never suggested that mobile phone alarms were involved in the detonation of the explosive devices.

If mobile phones had been used, it would lend weight to the theory that the bombers did not know they were being used as suicide bombers by a terrorist mastermind.

Prof Hans Michels, an explosives expert at Imperial College London, said: “Suicide bombers do not need timers to set off their bombs, nor do they need alarm signals from mobile phones, as they are likely to set off their deadly weapons themselves once they are in their dreadful target scenario.”

At a briefing for business leaders on Wednesday evening, Raymond Kelly, New York police commissioner, said the bombs were made from “hardware store” materials such as hydrogen peroxide hair bleach, citric acid and heat tablets used for cooking by the military.

He said the materials were used to make hexamethylene triperoxide diamine (HMDT), a more volatile explosive than the triacetone triperoxide (TATP) first believed to have been used. “In the flophouse where this was built in Leeds they had commercial grade refrigerators to keep the materials cool,” Mr Kelly said.

Scotland Yard would confirm only that the explosives were home-made, indicating annoyance at the leak of information from the US. New York police had said they were cleared by UK authorities to present the information but later admitted it should not have been released. However police in London said that was “not how things were understood” here.It is the second time the Met have been infuriated by US leaks. Pictures of bomb-making material given by the Met to US law-enforcement agencies were leaked to an American broadcaster.

In London, as another massive police operation deployed more than 6,000 officers to key locations across the city, a senior police officer warned yesterday the heavy security on the capital’s transport network would have to continue for a “long, long time”, in spite of the mounting costs that are putting a strain on police budgets.

Deputy chief constable Andy Trotter of British Transport Police said the capital would have to get used to “a different normality”. Commuters saw the now-familiar “nervy Thursday” ritual of armed police patrolling Tube and rail stations four weeks after the July 7 blasts which killed 56.

Speaking outside Russell Square station, which opened for the first time since the July 7 bombings, Mr Trotter said: “This is the biggest threat London has faced in peacetime and we have to throw all our resources into it. Today is part of getting London back to normality. It will be a different normality from before. The level of security will have to change for a long, long time to come.”

Separately, detectives’ hopes of an early extradition for Hamdi Issac, the July 21 bomb suspect being held in Rome, were boosted as an extradition hearing date was set for August 17. Police were also seeking permission to continue to hold for questioning two other suspects, identified as Muktar Said Ibrahim and Ramzi Mohammed, who were arrested after an armed siege in London last Friday.

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