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Police will use controversial facial recognition software to scan crowds gathered at the Remembrance Sunday service at the Cenotaph.

Met Police will deploy real-time biometric tracking at the event, where thousands of veterans will march past the Cenotaph and crowds gathered to watch Prince Charles lay a wreath.

The move comes after an information watchdog revealed in September hundreds of thousands of innocent people’s faces are being held on an official police database.

Human rights groups have denounced the technology as discriminatory towards innocent people.

But the Met has said the use of the technology at the central London event is part of an ongoing trial, and is not related to serious crime or terrorism.

The technology works by using cameras to scan the faces of passers-by and flag up potential matches against a database of selected images.

It was revealed in September that 19 million custody photographs are on file on the Police National Database, though many are of people who have since been released without charge.

Officers have compiled a dataset of about 50 individuals known for obsessive behaviour towards public figures, according to The Observer.

The facial recognition cameras was allegedly used on Sunday to identify individuals on the list at the Cenotaph.

However, civil rights group Liberty has said the use of the cameras is “intrusive and intimidating”.

Martha Spurrier, director of Liberty, told The Observer: “There is no legal basis and no public consent for deploying this intrusive and intimidating biometric surveillance in public spaces.

Not only are the Met using it on our streets again, they are targeting people who have done nothing wrong, are not wanted for arrest and may have serious mental health issues.

These people have just as much right as anyone else to pay their respects on Remembrance Sunday.

“There’s a dark irony to the Met resorting to this on the day we remember those who died to keep us free.”

A spokesperson for the Met confirmed that the technology is being used at this year’s Remembrance event “as part of the Met’s ongoing trial to test the technology at a range of different events” to assess “how effective it is in identifying known offenders”.

In a statement the police authority said: “The database is populated with images of selected individuals whose attendance would likely compromise the security and safety of the event.

“Only those images which come up as a match to a targeted individual will be retained by police."

The Met confirmed that the deployment of the cameras is to test the biometric technology, which was implemented following consultation with information, biometrics and surveillance camera commissioners.

The Met added: “We have also previously engaged with Liberty and Big brother watch in relation to the trial."

There will be a public consultation once the trial is complete and the results have been analysed, the Met confirmed.

Facial recognition technology previously faced criticism from human rights groups after trials ran at Notting Hill carnival to spot troublemakers in the crowds.