Retail staff being filmed by members of the public without their knowledge or consent is an "increasing problem", a shop workers' union has said.

It comes after a sales assistant told the BBC he had appeared in a video uploaded to TikTok and YouTube by former TV presenter Michael Barrymore without being asked for his permission.

Barrymore often films videos, including trips to the shops and interactions with the public, via a small built-in camera on his smart glasses, and uploads them to his several million followers.

Although Barrymore's exchange with the staff member was good-natured, Jayne Allport from the union Usdaw said other filmed encounters the public have with shop workers can "get heated" and are "really concerning".

There is no suggestion that Barrymore and other users of the smart glasses who film in shops are committing a criminal offence, although their actions are a breach of data protection laws.

Barrymore has been asked for a response.

Speaking to BBC Radio 4's The Media Show, Allport noted some retail staff could have serious concerns about their occupation or location being made public because of their own personal circumstances.

She told presenter Katie Razzall: "They could be filming someone who has escaped an abusive relationship or violent past and they don't want anybody to know where they are."

Unlike filming in public places, shops are private premises where permission to take photos or film should be sought from the owner.

Sales assistants at work would generally be considered to have a reasonable expectation of privacy, and for their consent for any use of film or photographs of them to be obtained before they are shared.

But many social media users who film interactions may not be aware of the law on this.

Barrymore was a hugely successful TV presenter in the 1980s and 1990s, known for shows such as My Kind of Music, Strike It Lucky and Kids Say the Funniest Things.

But in recent years, he has become better known, particularly to younger people, for his videos on social media platforms, particularly TikTok.

They often show him doing everyday activities such as "munchie runs" to supermarkets or shopping malls, visiting restaurants or running other errands.

The videos are hugely popular, and often humorous or entertaining. But one staff member at a shop in England expressed concern after he appeared in a clip.

The sales assistant, who asked to remain anonymous, told the BBC that he had only found out Barrymore had filmed him on one visit to the store several days later.

"One of the customers comes in and she says, 'I've seen you on a video'," he recalled. "And I had no idea what she was talking about."

When he got home, he looked on social media and found the video he appeared in. "And I had to sort of go backwards and piece together what had happened."

He added he was clearly identifiable in the video and said nobody asked him for his permission to appear.

The shop worker's comments come during an ongoing debate about the use of smart glasses, several million pairs of which have been manufactured and sold in recent years by some of the world's biggest technology companies.

Meta's Ray-bans are currently the most popular on the market, estimated to make up more than 80% of all AI or smart glasses sales. But their increased use has also prompted safety concerns.

The retail worker who served Barrymore told the BBC: "Personally I wasn't unduly bothered because I don't have any particular reason to be unduly bothered.

"But I can see that there are situations in which you would be very bothered. Let's say I've just come out of a very abusive relationship. It's not particularly unusual that people have to move area to get away from somebody.

"And in those circumstances, there's a video on social media platforms where it's perfectly obvious where I'm working, and somewhat obvious what area, in which case I would've been very concerned indeed."

The worker said he "probably wouldn't have minded" being filmed, but that he would like to have been asked before the recording began.

Allport said such recordings were an "invasion of privacy", and in some situations can have a "massive impact on our members' mental health".

She said the "really concerning" cases were times when "the customer is disgruntled about something that's happened... they confront the shop worker, film and upload it in order to embarrass the retailer".

"If you can imagine going to work and then being confronted by someone, having a discussion with them that may well get heated, that being filmed and then it goes on to social media, you can just imagine how those shop workers are feeling about it, it can be absolutely devastating."

Asked what advice she would offer to Barrymore, Allport replied: " I would say, just take five minutes before you do the filming.

"Go into the store, explain to the staff what you're intending to do, and ask them if they mind starring in... his video.

"And I suspect quite a number of them won't mind at all," she added. "But it is common courtesy to ask for permission."