Police are facing calls to halt the use of facial recognition software to search for suspected criminals in public after independent analysis found matches were only correct in a fifth of cases and the system was likely to break human rights laws.

Academics from the University of Essex were granted access to six live trials by the Metropolitan police in Soho, Romford and at the Westfield shopping centre in Stratford, east London.

They found the system regularly misidentified people who were then wrongly stopped. They also warned of “surveillance creep”, with the technology being used to find people who were not wanted by the courts. And they warned it was unlikely to be justifiable under human rights law, which protects privacy, freedom of expression and the right to protest.

Similar facial scanning software is being used in shopping centres, where it is embedded in advertising hoardings to track the shoppers’ age, gender and even mood, and has been deployed by other police forces in Manchester, Leicester and South Wales – where it will be used this weekend at the Swansea airshow. Officers will be scanning for “persons of interest” and “other persons where intelligence is required” as well as wanted criminals, the force said.

Quick guide What is facial recognition - and how do police in the UK use it? Show Hide What is facial recognition? This is a catch-all term for any technology that involves cataloguing and recognising human faces, typically by recording the unique ratios between an individual’s facial features, such as eyes, nose and mouth. Why is it in the news? After a trial of the technology, London's Metropolitan police have said they will start to use it in London within a month. On Friday, the force said it would be used to find suspects on “watchlists” for serious and violent crime, as well as to help find children and vulnerable people. Scotland Yard said the public would be aware of the surveillance, with the cameras being placed in open locations and officers handing out explanatory leaflets. How is it used in policing? The technology greatly improves the power of surveillance. At the simple end, a facial recognition system connected to a network of cameras can automatically track an individual as they move in and out of coverage, even if no other information is known about them. At the more complex end, a facial recognition system fuelled by a large database of labelled data can enable police to pinpoint a person of interest across a city of networked cameras. Why is it controversial? Facial recognition frequently sparks two distinct fears: that it will not work well enough, or that it will work too well. The first concern highlights the fact that the technology, still in its infancy, is prone to false positives and false negatives, particularly when used with noisy imagery, such as that harvested from CCTV cameras installed years or decades ago. When that technology is used to arrest, convict or imprison people, on a possibly faulty basis, it can cause real harm. Worse, the errors are not evenly distributed; facial recognition systems have regularly been found to be inaccurate at identifying people with darker skin. But the technology will improve, meaning the second concern is harder to shake. This is the fear that facial recognition inherently undermines freedom by enabling perfect surveillance of everyone, all the time. The fear is not hypothetical; already, Chinese cities have proudly used the technology to publicly shame citizens for jaywalking, or leaving the house in their pyjamas. Alex Hern Technology editor

David Davis MP, a former shadow home secretary, said the research by Prof Peter Fussey and Dr Daragh Murray at the University of Essex’s Human Rights Centre showed the technology “could lead to miscarriages of justice and wrongful arrests” and poses “massive issues for democracy”.

“All experiments like this should now be suspended until we have a proper chance to debate this and establish some laws and regulations,” he said. “Remember what these rights are: freedom of association and freedom to protest; rights which we have assumed for centuries which shouldn’t be intruded upon without a good reason.”

The Neoface system used by the Met and South Wales police is supplied by Japanese company NEC, which markets the same technology to retailers and casinos to spot regular customers, and to stadium and concert operators to scan crowds for “potential troublemakers”.

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Scotland Yard insisted its deployments were legal and successful in identifying wanted offenders, and that the public would expect it to trial emerging technology.

Deputy assistant commissioner Duncan Ball said the force was “extremely disappointed with the negative and unbalanced tone of this report”.

The study will increase pressure on ministers to legislate to define how facial recognition can be used in policing and in the private sector. Its use by South Wales police is currently under judicial review, while the information commissioner, Elizabeth Denham, has criticised “a lack of transparency about its use” and Tony Porter, the surveillance camera commissioner, last year intervened to stop Greater Manchester police using facial recognition at the Trafford shopping centre.

The Home Office said it believed there was an adequate legal framework for its use and it supported police trials, but added it was reviewing ways to simplify and extend governance and oversight of biometrics.

Scotland Yard granted the University of Essex academics access to six deployments of the system between June 2018 and February 2019. It uses cameras fixed to posts or on a van, and software cross-checks face-scans of passersby against a “watchlist”.

The research found that police were too hasty to stop people before matches could be properly checked, which led to mistakes; watchlists were sometimes out of date and included people wanted by the courts as well as those considered “at risk or vulnerable”; and officers viewed the technology as a way of detecting and deterring crime, which the report argued could have been achieved without biometric technology. They said it was “highly possible” Scotland Yard’s use would be ruled unlawful if challenged in court.

“While we focused on the police, by far the greater use is in the private sphere,” said Professor Fussey. “There’s a lack of any national leadership on this issue of facial recognition. Human rights standards should be embedded from the start in the use of technology.”

Of 42 people flagged up during the Met’s trials, 22 people were stopped, but of those only eight were being sought – some of whom were wanted for serious violent crime. Some were stopped for a crime the courts had already dealt with, but were arrested for a more minor offence that would not normally be considered serious enough to be tackled using facial recognition.

The Essex researchers also raised concern about potential bias, citing US research in 2018 into facial recognition software provided by IBM, Microsoft and Face++, a China-based company, which found the programmes were most likely to wrongly identify dark-skinned women and most likely to correctly identify light-skinned men.

In future, facial recognition software could screen images from body worn cameras and existing CCTV cameras, they said. This could allow a record of an individual’s movements, which could be analysed automatically to identify “unusual patterns of movement, participation at specific events, or meetings with particular people”.

Liberty, the civil rights campaign group, has previously called facial recognition “a dangerously intrusive and discriminatory technology that destroys our privacy rights and forces people to change their behaviour”.