A number of bombs and components, some packed with nails to cause death and maximum injury, were recovered from a car parked by the July 7 bombers at Luton station.

Senior sources told The Times that the devices recovered at Luton are “strikingly similar in their configuration and contents” to the unexploded bomb found at Warren Street Tube station on July 21.

The nature and number of bombs point to the existence of a large and well-equipped terrorist cell intent on a sustained campaign of attacks.

The quantity of ordnance found in West Yorkshire, Luton and London has heightened police concerns that there are many more than eight men willing to die as “martyrs”.

Frightening images of the devices left at Luton were published last night. The pictures, taken by scenes of crime officers, were leaked in the United States after they were shared by Scotland Yard with American law enforcement agencies.

The most graphic is an X-ray image of what explosives experts say was probably the “initiator” for the rucksack bombs. It shows a plastic bottle containing an improvised detonator attached to an electrical cable, along which a low-level current would have been sent to cause the explosion.

Felt-roofing nails, with their tips pointing outwards, are fixed to the outside of the bottle. The device would have been made into a larger bomb by surrounding it with cakes of high explosive. The nature of the recovered devices provides concrete evidence of a direct link between the July 7 suicide squad, whose four bombs killed 56 people, and the July 21 unit whose four devices failed to detonate.

A security source said: “This completes the circle. The bombmaker used the same constituents in the devices used in the fatal first attacks and the abortive attempts a fortnight later.”

Security sources last night said that the device found by a member of the public in Little Wormwood Scrubs, northwest London, after last Thursday’s failed attacks was a nail bomb.

Yesterday, the man identified by Scotland Yard as the prime suspect for the attempted bombing at Warren Street, Yasin Hassan Omar, was arrested in the Hay Mills area of Birmingham. Omar, 24, a Somalian who has lived in Britain since he was 11, was disabled by a 50,000-volt charge from a Taser stun gun.

He was last seen, on the Friday after the failed attacks, at his council flat at Curtis House, North London, which was used as a bomb factory.

It is believed that Omar and other members of the cell, including Muktar Said-Ibrahim, went there to rearm with new devices and to plan another attack.

Firearms officers were on hand for the 4.30am raid in which Omar was arrested. But detectives were determined to take him alive and no firearms were discharged.

He was driven straight to London where he is being held for questioning at Paddington Green police station.

Omar’s arrest and the discovery of such a large cache of bombs show that the al-Qaeda cell behind the London attacks is larger than was first thought.

The flat where Omar was found is thought to have been used as a safe house by the bombers for months. Witnesses have reported seeing a number of men matching the descriptions of the July 21 bombers at the address. Its existence suggests a wide support network for the bombers.

Three other Somali men were arrested at a house two miles away. Police want to establish if they are connected in any way to the bombers.

West Midlands Police, who moved out 20,000 people from Birmingham city centre on July 9 amid fears of an attack, are anxious to establish if the cell was actively planning bombings in England’s second city.

A second set of pictures leaked to the American media showed the extent of the damage caused by the explosion in the Piccadilly Line train at King’s Cross on July 7.

Jermaine Lindsay, 19, a Jamaican-born convert to Islam, killed himself and 26 passengers in the blast. The picture of the carriage’s interior shows the aftermath of a fierce explosion in a confined space.

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