The devices were intended to go off simultaneously at about 1pm, exactly two weeks after the devastation of July 7: at Warren Street, Oval, Shepherds Bush and on a bus in Hackney. As before, the attacks were aimed at the four corners of the London compass. Once again, each line attacked passed through King’s Cross.

But whereas the bombs on July 7 targeted London’s commuters at the height of morning rush hour, killing 56 people, yesterday’s attacks seemed intended for very different victims: the tourists, shoppers and schoolchildren using the transport system at midday.

The lack of mass casualties seemed to be the result of incompetence rather than restraint on the part of the bombers. Sir Ian Blair, the Metropolitan Police Commissioner, said that there was little doubt the intention “must have been to kill”.

Streets were cordoned off, much of the Underground system was paralysed and mobile telephone networks groaned under the strain as thousands of Londoners called friends and relatives, fearing a repetition of the carnage, and the anxious uncertainty, of a fortnight ago.

There was speculation that the blasts were caused by detonators, not bombs, and some witnesses on trains told of seeing rucksacks that had exploded but caused little damage.

At first, there was panic. Sofiane Mohellavi, 35, was readingwhen his carriage, then at Warren Street, was filled with the stench of burning rubber. “Suddenly people started screaming and were walking on each others’ backs trying to get out of there. I couldn’t move, I didn’t know what to do, whether to run or not.”

Witnesses saw a man carrying a rucksack, which suddenly exploded. “It was a minor explosion but enough to blow open the rucksack. The man then made an exclamation as if something had gone wrong. At that point everyone rushed from the carriage,” Ivan McCracken said. Initial reports suggested that the explosive device at Warren Street was a nailbomb, injuring one person.

Tammie Landau, 20, a secretary from Edgware, North London, said the smell of burning permeated her carriage, prompting passengers to bang on the windows with their hands and shoes, trying to smash the glass. “People were desperate. You just remember all those images from two weeks ago and need to get out,” she said. Once the doors were opened, she said, a number of people were trampled.

The three Tube bombs on July 7 detonated within 50 seconds of one another, while those yesterday were “almost simultaneous”, according to police. Passengers on the Oval train said they heard a sound like a balloon “popping”, followed by white smoke. When the train pulled into the station, a man leapt from the carriage and was seen running away, leaving behind a rucksack.

“We pulled into Oval and we all got off on to the platform. The guy just ran and started running up the escalator. Everyone was screaming to stop him,” one witness said. Another told of a tussle between the bomber and passengers: “There was one man struggling with three other men on the Tube over a rucksack. There was a woman and a baby standing next to them and crying.”

Shepherds Bush station on the Hammersmith and City Line was evacuated by police at 12.25pm after an apparent attempt to set off an explosion on a train, then on an overground section of track. Soon after, police appeared to be examining a package inside the front entrance. A witness described seeing a large cloud of dust coming from the direction of the station. Dozens of armed police and dog handlers arrived at the police cordon to begin searching sealed-off streets.

The No 26 bus was on Hackney Road, one of the main roads in East London, when the driver heard a loud bang followed by the smell of smoke. Mark Maybank, 38, stopped, shouted for everyone to get off and went upstairs to investigate. It was 1.30pm.

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