Similar components from the explosive devices have been found at all four murder sites, leading detectives to believe that each of the 10lb rucksack bombs was the work of one man. They also believe that the materials used were not home made but sophisticated military explosives, possibly smuggled into Britain from the Balkans.

“The nature of the explosives appears to be military, which is very worrying,” said Superintendent Christophe Chaboud, the chief of the French anti-terrorist police, who was in London to help Scotland Yard.

News of the breakthrough comes as a Times poll conducted in the aftermath of the bombings indicates that an overwhelming majority of the British public favours a tough approach to terrorist suspects. Almost 90 per cent of people want the police to be given new powers to arrest people suspected of planning terrorist acts, tighter immigration controls and strict baggage inspections.

Londoners, who bore the brunt of last Thursday’s carnage, were not as supportive of draconian measures as people in the rest of the country.

The public anger will strengthen Tony Blair’s hand as he prepares to speed up new anti-terrorist laws to help the hunt for the bombers. “If, as the fuller picture about these incidents emerges and the investigation proceeds, it becomes clear that there are powers which the police and intelligence agencies need immediately to combat terrorism, it is plainly sensible to reserve the right to return to Parliament with an accelerated timetable,” he said.

More than 800 police officers were being drafted in to assist Scotland Yard’s anti-terrorist branch in Britain’s largest criminal inquiry. Film from 2,500 CCTV cameras in the centre of the capital is being examined and more is being taken from cameras across Greater London. Detectives are also searching for a vehicle, flat or garage that the terrorists may have used as a bomb factory.

It is understood that the examination of the No 30 bus at Tavistock Square has yielded vital fragments that have sharpened the focus of the police inquiry. Forensic pathologists have been paying particular attention to the remains of two bodies found in the mangled wreckage of the double-decker.

A senior police source said: “There are two bodies which have to be examined in great detail because they appear to have been holding the bomb or sitting on top of it. One of those might turn out to be the bomber.” A decapitated head was found at the bus scene which has been, in Israeli experience, the sign of a suicide bomber.

The confirmed death toll stands at 52 but is expected to rise. Police family liaison officers have been assigned to 74 families. As London prepares to hold a two-minute silence and mass vigil on Thursday to commemorate its dead, 12,000 United States service personnel have been ordered not to visit the city for security reasons.

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