The friend of Shezhad Tanweer, the Aldgate bomber, alleges the fifth man pulled out of the attacks just hours before the terrorists embarked on their mission.

The claims will be investigated this week by detectives from the Metropolitan police who are compiling evidence on possible co-conspirators.

The fifth man, it is claimed, would have used the bombs left behind in a rucksack beneath a seat of the terrorists’ car at Luton railway station.

Although the unused bombs were less powerful than the four devices that killed 52 people, their purpose has never been satisfactorily explained.

The alleged fifth terrorist — who has been named to The Sunday Times — is in his thirties and, like three of the bombers, is British-born with Pakistani parents. He is known to Scotland Yard’s 7/7 team, based in Bradford, but has not been interviewed by them.

The claims were made in a series of interviews with the friend of Tanweer, who describes the Aldgate Tube bomber as being “like a brother”.

The friend, who lives close to Tanweer’s home in Beeston, Leeds, learnt of the fifth bomber’s identity after the attacks. He says the man admitted his role to a member of his family. “They [the four suicide bombers] were supposed to meet him but he never turned up. Because they were on a time schedule they left without him. His brother had talked him out of it.”

Three of the bombers — Tanweer, Mohammad Sidique Khan and Hasib Hussain — left Beeston after 3am in a Nissan Micra to drive to Luton railway station. They then took a train to London, leaving the unexploded bombs behind in the rucksack. “They [the bombs] were supposed to have been for him but when he didn’t turn up they just left it [the rucksack] there,” said the friend.

He said the fifth bomber’s identity was known to a handful of people in Beeston. “There are people who know . . . but nobody wants to say.”

The Home Office’s official report on the July 7 attacks concluded that “there is no intelligence to indicate that there was a fifth or further bombers”.

But police are not ruling out the possibility there may have been co-conspirators.

There also remains the mystery surrounding the unexploded bombs. They were made of peroxide just like the exploded bombs and have been described by police as “viable devices ready to go off”. They were, however, smaller and contained nails.

Hans Michels, an explosives expert from Imperial College London, believes the devices were “boosters” that would be used to trigger bigger explosives. Large solid blocks of peroxide explosive were also found in the car.

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