Legally allowed to work during this time, they mostly take on menial jobs like salad packing or working as labourers, earning an average of £10 (R105) a day.

But if they take part in a day-long shoot for a pornographic film, they can earn between £250 for a "girl on girl" scene and £400 for a "double penetration" scene.

The owner of Beehive Studios in Britain, who did not want to be named, admitted on Friday that he hired "many young" South Africans to work in the adult entertainment industry.

"You have to be young to be in this business and we get a lot of South Africans working with us. We find they are professional and do have a good work ethic."

"Mike", from F1 Studios, a "glamour" model agency, said "it probably pays better than picking cabbages".

An adult-film producer at Candice Paris confirmed his company had employed South Africans.

"Our actors are well-paid according to industry standards."

Richard Kunzmann, a freelance writer and author of an article featured in South Africa's Student Life (SL) magazine, which highlighted how young South Africans were involved in the UK's porn industry, said he discovered the story at a book launch while he worked in a bookstore in the UK.

"I was invited to a book launch and it turned out to be the launch of British porn director Anna Span's guide to home adult movie-making.

"A month later, a South African friend of mine was commissioned to write the script for a porn movie. That's when I started exploring the subject some more, and soon found out that there are some very professional South African actors on the circuit.

"It is certainly a very, very lucrative business to get into in the short term. A lot of gap-year people heading to London are sorely disappointed when the prospects they were promised back home aren't that golden," he said.

"They end up in dead-end jobs, earning a pittance as security guards or barmaids.

"So, when these young people page through student magazines over there and see adverts for glamour models or maybe are approached by an adult-movie agent, they might jump at the chance to make more than £500 in less than two hours - particularly if they have an exhibitionist streak in them."

South African porn actors, Kunzmann said, "fear being exposed for what they're doing to try to earn good money and bring home that big London dream".

"They don't want their parents, friends and family finding out about it. That scriptwriter told me he'd maybe let his mother know what he was doing if he became a rip-roaring success.

"South Africa is very much a purist and restricted society, and a lot of young people long to let it all out, physically or otherwise."

He said he knew of a "retired" starlet in South Africa who had made it big and and was still working in the sex industry, but has still not given her identity away, "even though she has fan websites dedicated to her".

Most South African adult film stars working in the UK are in their mid to late twenties, he said, and are white.

"There is a South African couple I know of who are known for their daring acts in front of the camera, and are therefore in very high demand.

"They've already bought two houses in South Africa, pretty much hard cash, and live very comfortably here and in the UK... I guess when you don't get taxed on the sums you make, that certainly helps."

There are at least 40,000 young South Africans living legally in Britain at any time.

Each year, the British High Commission in Pretoria issues 20,000 working holiday visas to South African applicants, according to Russ Dixon, head of the high commission's media section.

Successful applicants, who will be allowed to stay in Britain for an extended holiday of up to two years, have to be Commonwealth citizens aged between 17 and 30.

Pornography is not a crime in the UK, according to the British Home Office, only "extreme pornography".

A spokesperson for the London Metropolitan Police laughed when she was asked whether police would arrest porn actors, suggesting the crime was considered too trivial to prosecute.

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