New details have emerged of the "ball-bearing" bombs designed by the 7 July terrorist cell, which aimed to cause mass casualties.
The devices, consisting of acetone peroxide packed into jam jars wrapped with a band of metal, were found in a car rented by the suicide bomber Shahzad Tanweer. It was left at the car park of Luton railway station.
Meanwhile, it was reported last night that an al-Qa'ida suspect wanted in connection with the London bombings had been arrested in Zambia. Haroon Rashid Aswat, a British national who grew up in West Yorkshire near the 7 July bomber Mohammad Sidique Khan and is also wanted by the US authorities for his alleged role in setting up a military training camp in Oregon, is said to have been held for more than week.
The bombs found at Luton, which could be lit by a fuse, are believed to have been intended for the next stage of the terror campaign. They were similar to nail bombs made out of milk bottles, also found.
Another type of bomb discovered in the cache, peroxide in a bottle with a fuse at the top, is thought to have been for use as a "charger", to set off a larger bomb.
The discovery, five days after the first attack on London, shows that the terrorists had manufactured an array of bombs with different capabilities intended to change their pattern of attack. What united them was that the general public was likely to be the main target.
Robert Ayers, an explosives expert with 30 years of experience with the US Army and the British military, said: "It appears that the bombers were thinking ahead and had prepared a range of devices which could be used either as they are or adopted for other use.
"The nail bombs were anti-personnel weapons meant to cause horrific injuries or deaths. One lot in the new photographs are similar, with the ball bearings acting as the shrapnel instead of nails. The other ones could be turned into that easily by adding metal, or to detonate a larger bomb."
The photographs of the bombs first appeared on American television channel ABC, with unconfirmed reports that they were supplied by members of an American team which has flown in to help British investigators. The Metropolitan Police Commissioner, Sir Ian Blair, said he was worried that colleagues had leaked the pictures. He added: " We have made our concern known."
On the position in Zambia, a Foreign Office spokesman could not confirm whether Mr Aswat had been arrested. He added, however: "We are currently seeking consular access to a British national reported to be in custody in Zambia."
Mr Aswat, 30, is believed to have been in Britain in the days before the 7 July attacks and apparently left just hours before the explosions. Investigators discovered some 20 calls had been made from his mobile phone to two of the four men, according to reports. A US official, who spoke on condition of anonymity, said that British and American anti-terrorism investigators had travelled to Zambia and were in talks with officials about where best to prosecute him. It was reported that British authorities denied a US request to detain Mr Aswat just weeks before 7July.