Silkie Carlo, director of Big Brother Watch, has filmed the police on numerous facial-recognition deployments. She was there the night Shaun Thompson was picked up by police.

“My experience, observing live facial recognition for many years, [is that] most members of the public don’t really know what live facial recognition is,” she says.

She says that anyone’s face who is scanned is effectively part of a digital police line-up.

“If they trigger a match alert, then the police will come in, possibly detain them and question them and ask them to prove their innocence.”

The use of facial recognition by the police is ramping up.

Between 2020 and 2022 the Metropolitan Police used live facial recognition nine times. The following year the figure was 23.

Already in 2024 it has been used 67 times, so the direction of travel is clear.

Champions say that misidentifications are rare.

The Metropolitan Police say that around one in every 33,000 people who walk by its cameras is misidentified.

But the error count is much higher once someone is actually flagged. One in 40 alerts so far this year has been a false positive.

Michael Birtwhistle, head of research at the Ada Lovelace Institute research group, believes the technology is so new that the laws have not yet caught up.

“I think it absolutely is a Wild West at the moment. That’s what creates this legal uncertainty as to whether current uses are unlawful or not,” he says.

In Bethnal Green, although some people the BBC spoke to were worried about the use of the tech, a majority were supportive – if it helped to tackle crime.

That leads to another question about the technology: will it help in the long run?

As people get more used to seeing white vans parked on busy high streets, will people who know they are wanted by police simply get wise to the cameras and avoid them? Will shoplifters hide their faces?

Ms Carlo says society needs to guard against facial recognition becoming normalised.

“Once the police can say this is OK, this is something that we can do routinely, why not put it into the fixed-camera networks?”

This is the dystopian future that civil-liberty campaigners are most afraid of – a China-style mass-surveillance state.

Advocates dismiss such dire predictions as overblown.

And it is also clear there are plenty among the public who are willing to put up with having their faces scanned – if it means safer streets.