Children are posting videos on the internet showing them choking other youngsters to the point of collapse, in a craze that doctors warn has led to brain damage and death.
In one, a group of teenagers set out clear guidelines to the practice in an "instructional video", while in several others British voices can be heard.
The problem has been increasingly acknowledged in the United States, Canada and France but campaigners warn that Britain is turning a blind eye. The craze is spreading on the internet largely without the knowledge of adults.
"This is disturbing, highly dangerous, very risky and the practice should be avoided at all costs," said Professor Steve Field, chairman of the Royal College of General Practitioners. The American Centres for Disease Control and Prevention warned recently: "Parents, educators and healthcare providers should become familiar with warning signs that youths are playing the choking game."
In Britain, the Department for Children, Schools and Families said it was aware of the activity and was monitoring the situation closely. There is no authoritative research on the issue in the UK, despite campaign groups compiling 86 cases of young people in Britain who may have died this way.
Known by a variety of names from funky chicken to space monkey, the "game" involves hyperventilating or squeezing the carotid artery in the neck for a few seconds to achieve a high. Constricting the artery cuts blood flow to the brain; when the pressure is released, the resulting rush of oxygen causes the high. Experts say it is most prevalent among high-achieving adolescents who do not want to get in trouble by taking drugs or drink. The practice is different to autoerotic asphyxiation because it is not done for sexual gratification.
In the troubling footage on YouTube, British teenagers can be seen losing consciousness, their eyes rolled back, as they collapse to the ground to the sound of their friends' laughter.
The videos show teenagers applying pressure to the necks of friends. Others try to create the high on their own, using a ligature, with a greater risk of killing themselves if anything goes wrong and help is not at hand.
One American entry on MySpace, to background rap lyrics of "spaz if you want to", claims to be an "instructional video" on the different ways of playing the "pass-out game" and shows different teenagers collapsing among their friends.
Anne Phillips, who lost her teenage son to the practice, is trying to raise awareness in Britain. She says that while the problem has been acknowledged by the authorities in several other countries, the UK remains in denial. "It becomes addictive and kids progress to using a ligature for greater effect," said Mrs Phillips, from Somerset. "Deaths by hanging are put down as suicide or as an open verdict because coroners are not looking for this as a cause," she added.
This month, France's Ministry of Health hosted an international symposium on the "jeu du foulard" ("scarf game"). Politicians and doctors heard from teachers, paediatricians, police, psychologists and grieving parents from around the world.
In July last year, police in Swansea investigated a case where a 13-year-old at Ysgol Bryn Tawe school collapsed after apparently playing the choking game. Days later an eight-year-old at another school also reportedly had to be revived. Last August parents at Hardenhuish School in Chippenham, Wiltshire, were warned of the dangers. Deputy head Jan Hatherell explained that the school felt it was its social responsibility: "We got wind of the fact that some of our young people had seen this on the internet and had thought about trying it out on themselves.
"As yet, we do not know of anyone locally being injured from this, but our concern remains that they might be."
On one website a girl using the name Tiltal described how she had fainted while playing the game and "like shaking, was it a fit? and my eyes were open and rolling back and stuff is this normal? when i woke up i had no idea what happened and i didnt feel high or anything... and now everyone is doing it at school and apparently if i was doing all this i could of died, is that true? im trying to get everyone to stop doing it now, what could i say?"
Doctors warn the choking game can lead to seizures, head injuries, strokes, heart failure and brain damage. Parents are warned to look out for unexplainable headaches, bruising round the neck, bloodshot eyes or ear pain.
A spokeswoman for the Department for Children, Schools and Families said officials were aware of the activity: "Through the UK Council for Child Internet Safety, we will continue to work with the internet industry to keep young people safe online, including through reducing the availability of harmful and inappropriate content."
Last year the US Centres for Disease Control and Prevention (CDC) estimated that at least 82 young people had died in the US from the choking game between 1995 and 2007, of whom 87 per cent were boys. The average age of the victims was just over 13, and most had been playing alone.
But the campaign group Games Adolescents Shouldn't Play claims that as many as 458 children in the US have been killed this way, and that 86 British youngsters have died because of the craze since 1995.
The CDC admitted it had only tracked the problem through newspaper reports and had not included cases where the cause of death might have been either unintentional or intentional strangulation. A 2008 Centre for Addiction and Mental Health study found that 79,000 students in the Canadian province of Ontario had participated in the practice, while last year a survey of Texas students found that 68 per cent had heard of the game and 45 per cent knew someone who had played it.
Mrs Phillips, who has four other children, said: "There is no research being done in England. This issue needs to be addressed; parents need to know.
"It is a global problem but in England there is a denial. There is a stigma. Everyone is afraid that if you mention it, it is going to give kids ideas. But they already know about it ... As a parent I am fighting because I want to make sure that something worthwhile comes out of the death of my child."
Both YouTube and MySpace said they remove unsuitable content when it is flagged by other users. YouTube said: "Sadly, as with any form of communication, a tiny minority of people try to break the rules. On YouTube, these rules prohibit content like pornography or gratuitous violence."
A MySpace spokesman insisted it had "robust procedures in place to protect young people".
Mrs Phillips was living in Canada 16 years ago when her son Mike, 18, who had planned to study mechanical engineering at university, died after he and his friends played the fainting game.
He passed out, hit his head on a kerb and suffered such severe brain damage that he never recovered from a coma. His friends insisted he had slipped, but the police later discovered they had been playing the game. His mother, who returned to Britain after his death, said: "It's a long time since Mike died but sometimes it hits me as if it was yesterday. The whole family was messed up and when you know it is because of a game and was totally needless, it is particularly terrible."Reuse content