In addition to the huge cost of the damage, work in the City will be disrupted, with hundreds of office workers having to be rehoused. Restoring essential services, water, gas, and communications and computer networks will take time.
Businesses may not be able to occupy some of the more seriously damaged buildings for several months, but the Lord Mayor of London, Sir Francis McWilliams, said all the major businesses will be back at work tomorrow.
'The City of London will continue to work. There are risks everywhere in New York, Paris, Berlin and London but people will continue to come here, it's the place to be,' he said.
Clive Longhurst, of the Association of British Insurers, said some property owners would be breathing a sigh of relief that an agreement on insurance cover against terrorism had been reached with the Government.
The City of London Corporation yesterday began an emergency operation. Michael Cassidy, chairman of the policy and resources committee, said that after last April's Baltic Exchange blast, the corporation allocated extra cash for the City of London police to recruit 40 extra officers. 'We can't absolutely protect against these things. We're going to have to look at setting up more roadblocks. There will be more road closures,' he said.
The bomb would inevitably hamper the City's attempts to establish itself as an even more important financial centre. 'It is not helpful when we're promoting the City worldwide. All we can do is react appropriately by rehousing people and minimising disruption,' he said.
Property chiefs, including Stuart Lipton of Stanhope, had already been in touch with the corporation with offers of alternative office accommodation. Mr Cassidy said temporary rehousing would be found for those businesses needing it. He added that the availability of office space in the recession, which has hit the City hard, had minimised the economic cost of last year's bomb.
The Bank of England, which traditionally speaks for the City, believes that disruption to business in the Square Mile will be extremely limited and will not affect the City's standing.
'We can ensure that that we get things back to normal as quickly as possible,' said Eddie George, the governor-designate. 'We achieved a very quick recovery after the Baltic Exchange bomb and we will work with the police and the Corporation of London to do the same again.'
A Bank spokesman said: 'There is a strong motivation for firms to get back and trade, and there is plenty of high-quality office space available in the City for those in damaged buildings to move into.' He added: 'There is no evidence that these outrages have any impact on the City as a financial centre. No foreign banks were put off coming to London after the last bomb.'
A helpline for businesses was set up by the Royal Institute of Chartered Surveyors on 071 606 3030.