Police are to be given live access to London's congestion charge cameras - allowing them to track all vehicles entering and leaving the zone.
The congestion charge covers central London
Anti-terror officers will be exempted from parts of the Data Protection Act to allow them to see the date, time and location of vehicles in real time.
They previously had to apply for access on a case-by-case basis.
Home Secretary Jacqui Smith blamed the "enduring vehicle-borne terrorist threat to London" for the change.
Police are believed to have used the cameras to trace the routes taken by the two Mercedes cars used in last month's alleged attempted bomb attacks in London.
But the Home Office said discussions were underway on giving police greater access to data before the discovery of the two car bombs.
Under previous rules, police had to apply for access to the cameras on a case-by-case basis because of concerns that routine use of the information would be an invasion of privacy.
Under the new rules, anti-terror officers will be able to view pictures in "real time" from Transport for London's (Tfl) 1,500 cameras, which use Automatic Number Plate Recognition (ANPR) technology to link cars with owners' details.
But they will only be able to use the data for national security purposes and not to fight ordinary crime, the Home Office stressed.
Police and security minister Tony McNulty said: "The Commissioner of the Metropolitan Police believes that it is necessary due to the enduring, vehicle-borne terrorist threat to London.
"The Met requires bulk ANPR data from TfL's camera network in London specifically for terrorism intelligence purposes and to prevent and investigate such offences.
"The infrastructure will allow the real-time flow of data between TfL and the Met."
Mr McNulty said the home secretary had signed a certificate exempting the two organisations from some provisions of the 1998 Data Protection Act.
The Met will produce an annual report for the Information Commissioner, the government's data protection watchdog who oversees how material from CCTV cameras is used.
The scheme will also be reviewed in three months' time after an interim report by Met Commissioner Sir Ian Blair, so the home secretary can be "personally satisfied ... that the privacy of individuals is protected", added Mr McNulty.
Congestion charge cameras form a ring around central London to enforce the £8-a-day toll.
Although charges are only in force at peak times, the system runs 24 hours a day, a TfL spokesman said.