Police and alcohol charities have issued a warning about the dangers of an internet binge-drinking game after the deaths of two young men.
Isaac Richardson, 20, a former grammar school pupil, and 29-year-old Stephen Brookes, from Cardiff, are thought to be the first two Britons to die after taking part in the Neknominate game.
The craze involves participants filming themselves consuming dangerous amounts of alcohol before posting the results on social networking sites and nominating friends to outdo them. It is thought to have started in Australia and has been linked to several deaths, including two in Ireland.
Mr Richardson, who grew up in Colchester, Essex, is thought to have drunk a lethal concoction of wine, whisky, vodka and lager as part of an internet challenge on Saturday evening.
According to witnesses, he collapsed minutes later and was taken to hospital where he died shortly afterwards.
Police said his death was being treated as unexplained but not suspicious.
In South Wales, police confirmed that they were investigating the sudden death of Mr Brookes, who is thought to have collapsed after attempting to drink a pint of vodka. A video of him taking part in the challenge was uploaded onto Facebook on Saturday night, but is thought to have been removed after the news of his death became known.
A spokesman for South Wales police said: "We are investigating the sudden death of a 29-year-old man during the early hours of February 9.
"Officers have received information regarding the so-called neck and nominate game."
Mr Brookes's mother Paula described her son as kind and generous and said he was loved by everyone who met him.
His friends urged others not to participate in the controversial drinking craze and warned that there would be more loss of life.
Eric Appleby, the chief executive of the charity Alcohol Concern, said: "This lethal 'game' shows just how hard we have to work to de-normalise binge-drinking among young people.
"But it's not just about young people. They take their cues from society's attitude to drinking and it's this we have to change for all our sakes."
Another alleged participant in the craze narrowly avoided serious injury when he fell into the road after being filmed attempting to open and drink a bottle of beer while cycling with no hands.
Ross Fawcett, 21, lost almost a pint of blood from a gash to his hand after losing his balance while cycling through Ipswich.
There have been calls for Facebook to ban users from posting videos of themselves taking part in Neknomination.
The site said it did not tolerate comments which were directly harmful but added that controversial behaviour was not against its rules.