London police say they will start using live facial recognition cameras in operational deployments, in a major advance for the controversial technology.

Key points: London already has one of the highest concentrations of CCTV cameras in the world

London already has one of the highest concentrations of CCTV cameras in the world Rights groups say the technology threatens basic civil liberties

Rights groups say the technology threatens basic civil liberties Police have previously trialled facial recognition in the British capital

The Metropolitan Police Service said it would use the cameras to automatically scan the faces of people passing through small targeted areas where intelligence suggested serious offenders would be found.

It did not say how many areas, or how many cameras would be deployed.

Real-time crowd surveillance by police in the British capital is among the more aggressive uses of facial recognition in wealthy democracies and raises questions about how the technology will enter people's daily lives.

Authorities and private companies are eager to use facial recognition, but rights groups say it threatens civil liberties and represents an expansion of surveillance.

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London's decision to use the technology defied warnings from rights groups, members of parliament and independent experts, Amnesty International researcher Anna Bacciarelli said.

"Facial recognition technology poses a huge threat to human rights, including the rights to privacy, non-discrimination, freedom of expression, association and peaceful assembly," she said.

London police said the facial recognition system, which runs on technology from Japan's NEC, looks for faces in crowds to see if they match any on "watchlists" of people wanted for serious and violent offences, including gun and knife crimes and child sexual exploitation.

"As a modern police force, I believe that we have a duty to use new technologies to keep people safe in London," Assistant Commissioner Nick Ephgrave said in a statement.

London police previously carried out a series of trial deployments of the technology.

But University of Essex professors who monitored them said in an independent report last year that the trials raised concerns about the legal basis and the accuracy of the equipment.

The British have long become accustomed to video surveillance, with cameras used in public spaces for decades.

Real-time monitoring will put that tolerance to the test.

London is the sixth most monitored city in the world, with nearly 628,000 surveillance cameras, according to a report by consumer technology website Comparitech.

The Met is not the only British police force using facial recognition technology.

The South Wales police force has been using it since 2017 to monitor crowds at big events like soccer games, royal visits and air shows.

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AP