The information watchdog has launched a formal investigation into the police use of facial recognition technology following trials across the country, The Daily Telegraph has learned.

Information commissioner Elizabeth Denham opened the inquiry after expressing “significant concern” over the legality and effectiveness of the technology, which was used at last year’s Notting Hill Carnival and Remembrance Sunday.

Earlier this year, Ms Denham threatened to launch legal action against the Home Office and the National Police Chiefs’ Council over concerns relating to the intrusive nature of the technology, which uses artificial intelligence to identify potential troublemakers by scanning thousands of faces recorded by surveillance cameras.

In a blog post earlier this year, Ms Denham said: “How facial recognition technology is used in public spaces can be particularly intrusive. It’s a real step change in the way law-abiding people are monitored as they go about their daily lives.