The Metropolitan Police has denied that use of its dubious facial recognition technology at the Notting Hill Carnival in London led to someone being wrongfully arrested.
The Brit force's denial contradicts an observer who spoke to constables operating the facial recognition system on the day.
News reports suggested that police use of facial recognition technology during the event led to at least one mistaken arrest and a slew of false matches.
The Liberty pressure group, which has long campaigned against police surveillance tactics, secured access to the police facial recognition van during the controversial West London festival, which has become notorious in recent years thanks to violence and illegal drugs.
A blog post by the pressure group's policy officer for technology, Silkie Carlo, said that the Met had assembled a list of 500 people it was hoping to catch with its facial recognition system. Constables operating the system told her it had recorded around 35 false positives, with five of those people being stopped.
One person was arrested, according to Carlo, on the basis that there was an arrest warrant out for them – though they were released when constables realised that the suspect had already been arrested and released and was no longer wanted on a warrant. This appears to be a policing admin problem rather than a problem with the facial recognition system itself.
"Between the construction of their watch list and Carnival, that individual had already been arrested... So they were sent on their way, after an unnecessary but seriously hi-tech arrest," wrote Carlo.
The Met would only admit to The Register that one person was "identified" and "spoken to" but denied they were arrested.
"We have always maintained that it was a continued trial to test the technology and assess if it could assist police in identifying known offenders in large events, in order to protect the wider public," said a Met public relations operative who gave her name only as "Camilla".
"Whilst we are trialling this technology we have engaged with the Surveillance Camera Commissioner, the Information Commissioner, the Biometrics Commissioners, and Big Brother Watch. Liberty were invited to observe its use at the Carnival this year," added "Camilla".
Liberty's Carlo also noted that the cameras for the facial recognition system had been concealed from the public, so as not to draw attention to the fact that the system was in use. Regarding how one of the people who was flagged up as a false positive could find that out, she wrote: "How that could be possible, given the 'strategic' concealment of the cameras and the fact she was not informed of the false match or that her photo was taken, is baffling."
The Data Protection Act 1998 gives people a legal right to demand copies of information held about them, including CCTV images and related data. It is estimated that around two million people enter the general area of the annual carnival.
As we reported before the carnival, privacy activists and human rights campaign groups had written to Met Commissioner Cressida Dick, urging her not to use the controversial technology. Research has previously revealed the inaccuracy of facial recognition technology. Hundreds of thousands of mugshots, mostly of innocent people not convicted of any criminal offence, are used to feed the Met's face-matching database. ®