The force had put out a statement saying “anyone who declines to be scanned will not necessarily be viewed as suspicious”. However, witnesses said several people were stopped after covering their faces or pulling up hoods.
Campaign group Big Brother Watch said one man had seen placards warning members of the public that automatic facial recognition cameras were filming them from a parked police van.
“He simply pulled up the top of his jumper over the bottom of his face, put his head down and walked past,” said director Silkie Carlo.
“There was nothing suspicious about him at all … you have the right to avoid [the cameras], you have the right to cover your face. I think he was exercising his rights.”