The package, found on Saturday morning, appeared to be packed with explosives, nails and bolts, similar to the device found at Warren Street. Police carried out a series of controlled explosions on it.

The four fugitives whose bombs failed to explode must know they cannot stay in one place for long. Their names are known to police, who are trying to find out if these are the men’s real identities. Many identification documents and other evidence had been cut into pieces but were carried in the rucksacks. Detectives are also studying telephone calls believed to link this cell with the four who blew themselves up on July 7.

It is not clear if these are direct calls between the two, but the hope is that they may reveal the identity of other key figures such as the bombmaker and the man who co-ordinated that operation. Detectives want to establish if this gang can lay their hands on more explosives. Police scientists are also trying to identify the chemical signature of the explosive left in the rucksacks and match it to bombs used on July 7.

FBI specialists have offered their expertise amid warnings these chemicals degrade and may be dangerously unstable. The bombers must realise this, so unless they have access to another supply there is an urgent need for them to use what may be left.

Police chiefs do not expect this gang to try to flee the country, even though all are believed to be of East African origin. One senior source told The Times: “These men seem determined to die. They are likely to have been picked for their stronger resolve than the four men who died on July 7.”

All four are likely to have gone their own separate ways last Thursday and none has been in touch with their families. A number of addresses are under surveillance, including those of other members of their cell who played supporting roles.

Police are investigating claims that both sets of bombers met at the National Whitewater Rafting Centre at Frongoch, near Bala, North Wales. It is thought that at least two from the bungled attack met Mohammad Sidique Khan and Shehzad Tanweer, who died in the first bombings. Police believe Khan organised the trip as a training course.

• Aldgate station, shut since July 7, reopens today, bringing a full service on the Metropolitan Line.

  The Circle line remains closed and the District is suspended between Edgware Road and High Street Kensington. Replacement bus services are in place on parts of the Piccadilly Line.

  A shuttle service will operate every 15 minutes on the Hammersmith & City Line between Hammersmith and Paddington.

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