Sunita Somvanshi
Matt Arnold just wanted to buy groceries. On August 6, the 46-year-old walked into his local Sainsbury’s in East Dulwich, London, scanned his items at the self-service till using his Nectar loyalty card, and left. A routine shopping trip. Except it wasn’t.
Unknown to him, Sainsbury’s facial recognition system had flagged him as a suspected shoplifter.
The technology, supplied by Facewatch, uses cameras to scan faces against a database of suspected offenders. When a match is found, an alert is sent to staff devices. Sainsbury’s claims the system has a 99.98% accuracy rate and every match is reviewed by a trained manager.
But something went wrong.
Management approached Arnold and told him he could not be served. “They came over and said I had to leave,” Arnold said. “The staff member said I’d been identified by the AI, and the cameras had flagged me.”
As he left, Arnold saw an overhead CCTV monitor with a red circle surrounding his face.
Sainsbury’s head office contacted Arnold the next day to apologise. The supermarket insisted the incident was caused by “human error,” not the facial recognition technology. Staff had targeted the wrong person after a separate flag, the company said.
Facewatch, the technology supplier, said a correct alert was sent to the retailer but was “subsequently subject to human error in the way it was handled in store.”
The incident was not the first of its kind. Another Sainsbury’s customer was previously wrongly challenged by the facial recognition system, also blamed on “human error.”
Arnold said the experience left him shaken. “What upset me was thinking this is what the future could be — people just listen to what the machine tells them to do without thinking about the consequences.”
Sainsbury’s has confirmed the technology has been paused at the Dulwich store while an investigation takes place. But the wider rollout continues across the chain.
Facewatch is used by more than 100 businesses across the UK. The company said the 0.02% margin is not a “real-world misidentification rate” but a boundary where human checks filter out errors.
But Arnold argues that even a tiny error rate becomes significant when millions of shoppers are scanned. “There are more people than me who have been caught out by this,” he said.
He donated a £150 goodwill voucher from Sainsbury’s to a local food bank. “If they’re suspending it in this East Dulwich store, they are conceding there’s a problem with it,” Arnold said. “Why aren’t they suspending it in every store?”
Silkie Carlo, director of civil liberties group Big Brother Watch, has called for Sainsbury’s to scrap the technology. “Serious mistakes like this are inevitable when a national retailer does hundreds of thousands of ID checks indiscriminately with this sinister surveillance tech,” she said.
Sainsbury’s began trialling facial recognition at some stores last year. The retailer highlighted British Retail Consortium figures showing 1,600 daily incidents of violence and abuse against shopworkers nationwide, up from 455 a day in 2019-20.
The initial trials across two stores resulted in a 46% reduction in logged incidents of theft and anti-social behaviour.
The supermarket said: “Customers can be reassured that the Facewatch system has a 99.98% accuracy rate, and every match is reviewed by a trained manager.”
But for Arnold, the damage is done. He said staff were “struggling to operate the system in a busy store environment” and were “not being equipped to implement the AI properly.”
The incident raises questions about the balance between security and privacy, between protecting staff and protecting customers from machines that can make mistakes.
