But now a new generation of cameras is beginning to be used. Like the one perched on the top of the Cardiff police van, these cameras feed into facial recognition software, enabling real-time identity checks — raising new concerns among public officials, civil society groups and citizens. Some members of Parliament have called for a moratorium on the use of facial recognition software. The mayor of London, Sadiq Khan , said there was “serious and widespread concern” about the technology. Britain’s top privacy regulator, Elizabeth Denham , is investigating its use by the police and private businesses .

And this month, in a case that has been closely watched because there is little legal precedent in the country on the use of facial recognition, a British High Court ruled against a man from Cardiff, the capital of Wales, who sued to end the use of facial recognition by the South Wales Police. The man, Ed Bridges, said the police had violated his privacy and human rights by scanning his face without consent on at least two occasions — once when he was shopping, and again when he attended a political rally. He has vowed to appeal the decision.

“Technology is driving forward, and legislation and regulation follows ever so slowly behind,” said Tony Porter , Britain’s surveillance camera commissioner, who oversees compliance with the country’s surveillance camera code of practice. “It would be wrong for me to suggest the balance is right.”

Britain’s experience mirrors debates about the technology in the United States and elsewhere in Europe. Critics say the technology is an intrusion of privacy, akin to constant identification checks of an unsuspecting public, and has questionable accuracy, particularly at identifying people who aren’t white men.