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 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.

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.