BRITAIN’S terrorist alert has been raised to its highest-ever level because the London rush-hour bombers are alive and planning another attack, The Times has learnt.

Security services, military and police are on “severe specific” alert — the second highest status and higher than after the September 11 atrocities — after it emerged that the terrorists who killed as many as 70 people were not suicide bombers.

The Times understands that the country’s biggest manhunt is focusing on evidence being gathered from King’s Cross station, which all three of the bombed Tube trains passed through on Thursday morning.

A re-examination of the timings of the explosions has revealed that the Underground bombs exploded within seconds of one another at 8.50am.

Investigators believe that the bombers assembled at the huge station, with its many rail connections, before dispersing to plant their devices around the Tube network.

The Circle Line bombs detonated when the Aldgate train was eight minutes east of King’s Cross and the Edgware Road train was eight minutes to the west. The Russell Square train was blown up seconds later, south of King’s Cross on the Piccadilly Line.

The bombers who killed 191 people in Madrid last year also gathered at one place before separating to plant devices timed to explode simultaneously.

Examination of CCTV footage from the dozens of security cameras around King’s Cross is a priority for investigators.

Scotland Yard also appealed yesterday for Tube passengers to send in mobile phone pictures and videos they may have made in the bombings. Streets and car parks near the station are being searched to discover if the terrorists left a vehicle.

The bombers travelled from outside London. “We believe they started out together, to ensure that there were no slips on the journey. Then they are likely to have split up to join separate trains,” a senior anti-terrorist source told The Times. “We need to find where these men were staying in the days before the attacks and where they collected the rucksack bombs.”

The other main line of inquiry is to recover forensic evidence from the mangled remains of the No 30 bus at Tavistock Square, where officers think a fourth bomber may have died at 9.47am.Police are trying to discover why his bomb — thought to have been of the same size and design as the Tube bombs — detonated 57 minutes after the synchronised devices.

One theory is that the man was to launch a second wave of attack, targeting people fleeing closed Tube stations.

When he found that stations had been quickly shut, the terrorist may have panicked, or been under orders to switch his attention to a bus, another symbol of London’s travel network.

One Scotland Yard source said: “We will never know for certain what happened in those last few minutes. He might not have woken up that morning as a suicide bomber, but circumstances meant he became one.”

Passengers on the bus noticed a 6ft tall, olive-skinned man, thought to be aged in his early 20s, looking agitated and rummaging in a rucksack.

Charles Clarke, the Home Secretary, said that the Government’s priority was catching the surviving bombers before they struck again.

The heightened security and a sense of nervousness has led to more than 100 bomb alerts, including the evacuation of 20,000 people from the centre of Birmingham on Saturday.

Three Britons were arrested under the Terrorism Act at Heathrow after being refused entry to the US but police said that they were not suspects. A US report that a Pakistani man was detained at Stansted on Friday, in possession of a marked Tube map, was dismissed.

None of the dead have been formally identified but autopsies have begun on 49 bodies. A further 31 people are listed as missing. London hospitals are still treating 62 injured, of whom 15 remain in a critical condition or in intensive care.

Police liaison officers have been sent to 59 families who fear that loved ones are dead or critically injured, while 31 families have visited an assistance centre for relatives of the missing.

The UK’s threat assessment level had been “severe general” until last month when, after the general election, it was dropped to “substantial”. After the rush-hour bombs, it has been raised two rungs.

The Metropolitan Police said yesterday that officers were looking into the firebombing of a Sikh temple and a number of other possible reprisal attacks in London since Thursday.

STATES OF ALERT

• Imminent Precise intelligence of a planned attack with timing and location known
  
  
• Severe specific Intelligence warning of a known terrorist plot
  
  
• Severe general A high possibility of attack at some stage but without knowledge of the timing or target
  
  
• Substantial Still a high alert but no intelligence of a specific plot

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