Police involvement in a private landlord's facial recognition trial has led a regulator to call for government intervention.
BBC Radio 4's File on 4 has learned that South Yorkshire Police shared three photos of serious offenders and one of a vulnerable missing person with Sheffield's Meadowhall shopping centre.
It follows similar controversial tie-ups in Manchester and London.
Meadowhall owner British Land said the 2018 test only lasted four weeks.
It added that it had "no plans" to use facial recognition at its sites, and that all personal data gathered during the trial was "immediately deleted".
South Yorkshire Police disclosed last August that it had "supported" the scheme to understand "opportunities associated with this technology," but did not provide further detail at the time. It has declined to comment further.
Privacy campaign group Big Brother Watch uncovered the added information about the Meadowhall scheme.
Tony Porter, the Surveillance Camera Commissioner (SCC) for England and Wales, has now called for government inspections into police use of facial recognition technology.
"I think if the public are going to be reassured, there does need to be a very clear oversight mechanism," Mr Porter told File on 4.
"And I would say that at the moment isn't obvious. I think the next step is for the government to address that gap in each and every circumstance that is required."
The Home Office's Surveillance Camera Code of Practice, which governs schemes involving both police and the private sector, states that "any use of facial recognition or other biometric characteristic recognition systems needs to be clearly justified and proportionate".
Former Brexit Secretary David Davis, who has been critical of police use of facial regulation, agreed that inspections are an "absolute necessity".
"You should no more give an absolute open sesame on personal surveillance, which is what facial recognition is, than you would give any police force the right to search you or your house without a warrant," he said.
The Meadowhall live facial recognition trial ran for four weeks between January and March 2018.
British Land told File on 4 it did not put up signs warning visitors that facial recognition was in use.
Big Brother Watch's director Silkie Carlo told File on 4 such partnerships are hard to monitor: "That means that this is even less accountable to the public and difficult to find details of.
"We're now at a stage where we think millions of people in this country could have been scanned by facial recognition, many of whom don't even know about it."
The Information Commissioner's Office (ICO) said it had considered the Meadowhall trial, but closed the case without taking further action.
Mr Porter, who oversees surveillance camera use by public bodies on behalf of the Home Office, still has unanswered questions and has requested a meeting with South Yorkshire Police.
A trial at the Trafford Centre shopping mall in Manchester in 2018 was halted after Mr Porter's intervention.
A scheme at the Kings Cross development in London, run between May 2016 and March 2018, is still being investigated by the ICO.
Big Brother Watch, Amnesty International, and the House of Commons Science and Technology Select Committee have all said automatic facial recognition technology should be halted until "proper regulation" that "explicitly regulates" the technology is in place.
Meanwhile, South Wales Police is continuing its use of the technology with a new trial of body worn facial recognition cameras that will begin in early spring.
The Home Office said it fully supports police trials of facial recognition, and is working alongside the Centre for Data Ethics and Innovation, who are exploring the issues around such schemes.
The ICO said the organisation has doubled in size over last three years, and their enforcement tools range from heavy fines to lighter sanctions, depending on the relative harm to individuals.
It's calling for a statutory code of conduct for police forces' use of live facial recognition,
"The regulation of live facial recognition (LFR) is a priority issue for the commissioner," it added.
"We have completed an investigation into police use of LFR, and there is ongoing work exploring how it is used by private organisations, including in airports."
File on 4's Facial Recognition: Who's Watching You? is on BBC Radio 4 on Tuesday 28 January at 20:00 GMT and available afterwards on BBC Sounds.