Blair, the Metropolitan police commissioner, has signed off a report by his force’s traffic unit which shows that black people account for 46% of all arrests generated by new automatic numberplate recognition (ANPR) cameras.

The technology allows car registration plates to be scanned and automatically run through databases to determine whether a vehicle is stolen, uninsured or has not had its road tax paid.

Each numberplate is also checked with the police national computer, where vehicles suspected of links to crimes such as robberies are flagged up.

The Met has deployed six mobile ANPR camera units in the capital, primarily in areas with high levels of street crime. When a suspect vehicle is identified, police officers are sent to intercept the driver.

Although ANPR technology is impartial, the disproportionate number of blacks being arrested has prompted the Met to investigate.

The arrests have been broken down by ethnicity in a report sent last month to the Metropolitan Police Authority (MPA), to which the force is accountable.

It reveals that between April 2005 and January this year the units generated 2,023 arrests. Of these 923 were black suspects, while 738 (36%) came from white backgrounds. Asians accounted for just over 9% of arrests.

The report tacitly appears to address concerns among ethnic minority communities who believe they are unfairly targeted by the police through stop and search powers. Black people are up to six times more likely to be stopped than whites.

The report says: “It is worth stating that out of all our activities, this is the one area where the officer has minimal discretion as they respond to an electronic matching process.”

Last week the Met attempted to explain the high number of arrests among blacks by the fact that they make up a higher proportion of the population in areas such as Southwark and Lewisham in south London, where the ANPR units operate.

However, statistics from the 2001 census show that the highest black population in any borough is no greater than about 25%. The proportion of black people across the capital as a whole is about 11%.

Peter Herbert, an independent member of the MPA and spokesman for the Society of Black Lawyers, said: “The Met really wants to avoid any allegation of disproportionality so they will seek to explain these figures by whatever nuance they can. The targeting of certain boroughs might be justified in terms of some crime, but it’s certainly not justified in terms of all crime.”

Captain Gatso, of Motorists Against Detection, the anti-speed-camera group that uncovered the Met figures, said: “All this does is create a new problem for Sir Ian Blair, the politically correct PC, as ANPR cameras and the databases they are linked to are colour blind.”

It is more than a decade ago that Lord Condon, the former Met commissioner, caused controversy when he suggested that young black men were likely to be responsible for most muggings.

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