The latest precautions are part of a pounds 5m package of permanent measures by the City of London Corporation and are expected to be introduced before the current temporary police measures are discontinued next July.
Other proposals include increasing spot-checks on vehicles, providing pagers for businesses and residents to warn them of danger, removing litter bins, and reducing the time refuse sacks are left in the street. Photographs of motorists would only be used for the prevention of terrorism, police said.
The measures are in addition to armed road blocks and other security measures put in force after the IRA bombing at Bishopsgate in April, in which a man died.
Colin Coxall, acting Commissioner for the City of London Police, said the temporary security measures introduced last month had already frustrated planned IRA attacks. 'We have firm information that we have deterred potential attacks on the City,' he said. 'We also have other intelligence that terrorist activities have been thwarted.'
Last November, when police activity was increased before the Lord Mayor's Show, a lorry loaded with explosives was stopped just outside the City, he said. In response to worries that the 'ring of steel' would be seen by the IRA as a challenge, he said: 'The alternative of doing nothing is unacceptable. There have been too many people injured or killed.'
An extra 93 officers have been working in the City since the Bishopsgate bombing and a system of security cameras covers the area. Mr Coxall said high-profile policing had proved successful. The overall crime rate went down 10.7 per cent last year and dropped by a further 16.4 per cent in the first six months of this year.