Police in London are to be able to track vehicles entering the capital by accessing congestion charge cameras as a result of the "enduring threat" of terrorist car bombings.

Ministers today lifted restrictions on access to the cameras to enable the Metropolitan Police to view images in "real time" from the 1,500 congestion charge cameras in the capital.

The sweeping change to data protection rules will allow Transport for London to transfer images in bulk from its cameras to the Metropolitan Police. The 1,500 cameras use automatic number plate recognition (ANPR) technology to link cars with owners' details.

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 on London.

Until today's announcement police had access to the congestion cameras only on a case-by-case basis because of concerns that routine use of the information would be an invasion of privacy. The Metropolitan Police will be able to use the data only for national security purposes and not to fight ordinary crime.

Tony McNulty, Minister for Policing, Security and Community Safety, said: “The Commissioner of the Metropolitan Police believes that it is necessary due to the enduring, vehicle-borne terrorist threat to London.”

He added: “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 that Jacqui Smith, the Home Secretary, had signed a certificate exempting the two organisations from some provisions of the 1998 Data Protection Act.

The Metropolitan Police will provide an annual report to Richard Thomas, the Information Commissioner, who oversees how material from CCTV cameras is used.

Mr McNulty added that the Home Secretary would also review the way in which the scheme is operating in three months’ time after an interim report by Sir Ian Blair, Commissioner of the Metropolitan Police.

The move was unveiled as the Home Office issued figures showing that more than 1,200 arrests have been made under anti-terror laws since the al-Qaeda attacks on the Twin Towers in New York in September 2001 and the end of March.

Only 41 people have been convicted under the Terrorism Act, plus 183 under other laws for murder, grievous bodily harm explosives and fraud offences.

The figures, which exclude Northern Ireland, show that a further 114 are either at trial or awaiting trial. More than half of those arrested were released without charge.

A detailed breakdown shows that of the 1,228 arrested, 132 were charged under terrorism legislation offences only and 109 with terrorism legislation and other criminal offences.

A total of 195 were charged under other legislation including for crimes of murder, grievous bodily harm, fireams and explosives offences.

Seventy-six of those arrested have been handed over to the Border and Immigration Agency, 15 are on police bail awaiting a decision about charges, 12 were cautioned and a warrant has been issued for the arrest of one person.

The figures show that 669 of those arrested were released without being charged by police.

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