Meanwhile, up to 10 people, men and women, detained by detectives in a series of raids yesterday were being held at central London police stations. They were being questioned about both the Bishopsgate bomb, which killed one man and caused massive destruction, and the two bombs that exploded in hijacked taxis on Saturday night.
Commander David Tucker, head of the Anti-Terrorist Branch said last night that both suspects were seen by a witness abandoning the tipper truck at 8.55am and walking south down Bishopsgate. The witness, who was unable to get a clear view of the men's faces, told police that they turned off to the left and may have been making for Aldgate Underground station near by.
He described the man who left by the driver's side as 5ft 8in to 5ft 9in tall, stockily built and wearing a three-quarter length slate-grey hooded anorak. The man who got out of the passenger side was about 5ft 9in tall, of athletic build and younger than his companion. He wore light blue trousers and a jean-style jacket of mottled white and blue on top of a hooded garment. Both men had their hoods pulled up.
Police have established that the eight-wheeled tipper truck had been stolen from a builder's yard near Newcastle-under-Lyme, Staffordshire, on 20 March. It had since been painted light blue and the registration number changed from D883 XFP to G430 DVT. Between then and the bomb being planted, police believe it is possible the public or a commercial spray shop may have seen it.
Detectives are also studying a video film which shows the IRA bombers leaving the lorry, but Mr Tucker said it was not expected that it would provide a clear image of the two men.
The camera was one of a number installed at strategic points in the City last year ater the Baltic Exchange bomb. Sources said the camera did not focus in at close range until after the first of the warning calls at 9.17am. Police are checking to see whether any other video cameras, sited on private buildings, filmed the bombers.
Owen Kelly, the City of London Commissioner, told a another press conference yesterday that the reason the bomb was not defused, despite the fact that police had identified it more than an hour before the explosion, was the fear that it was booby- trapped. 'It was a judgement of the bomb-disposal officer at the time.'
Mr Kelly repeated calls for changes to the Police and Criminal Evidence Act, which imposes strict guidelines over the way police carry out the armed road checks which the force introduced last December. Senior officers are concerned that the current checks are on the 'margins of legality' and could be open to challenge in the courts.
The force - which had its strength increased by 50 officers following last year's bomb - was temporarily moving officers from its large and respected fraud section to anti-terrorism duties.
Although, the Lord Mayor of London, Sir Francis McWilliams, will meet Kenneth Clarke, the Home Secretary, and John Major later this week to discuss boosting the City force, Mr Kelly said that it was 'not simply a question of resources'. 'We could close down the City and make it a very safe place, but it might not be a very pleasant or effective place to work in.'
Last night, Mr Clarke also said the City would not be turned into a 'fortress'. 'It would be very damaging to the reputation of the City of London to make all vehicles going in go through road blocks. We have to protect everywhere not just the last chosen target of the IRA.'
Mr Clarke stressed that the security forces were trying to keep 'ahead of the IRA' and dismissed criticism of the security measures by David Mellor, a former Cabinet colleague, and other 'armchair' critics.
John Major used a speech to bankers at the European Bank of Reconstruction and Development in the City to emphasise the importance of carrying on with 'business as usual'.
'For years terrorists in the UK have tried to bomb and murder their way to a political objective. They have won no sympathy for their cause and nothing but contempt for their campaign,' he said.
'On Saturday, they tried to maim the commerce of the City of London. They failed again . . . London has given its response. The markets are open. It is business as usual.'