Clubbers in Ibiza are being warned about a potentially lethal anaesthetic substance, known as liquid ecstasy, which is believed to be coming in from the UK.

BBC One's 4x4 Reports found as many as two coma patients a day are being treated in the island's main hospital for the effects of GHB - short for gammahydroxbutyrate.

Revellers can unknowingly overdose on the colourless, odourless liquid from water bottles passed around clubs.

GHB facts

Used as an anaesthetic in World War I Users may suffer sickness, stiff muscles, fits or comas Possession is currently not illegal but supply is Concerns have grown that sex attackers use the drug to sedate victims

Drugs charities say the people importing GHB to the island are putting less experienced users in danger.

Mat Southwell from Dance Drugs Alliance, who accompanied 4x4 on a research trip, said: "What's clear is this is a UK phenomenon.

"UK clubbers are bringing GHB out with them and possibly sharing it with other people and the inexperienced are getting into problems.

"If two people are in A&E every night with GHB overdoses it belies a much wider problem.

"Many more people will be knocking themselves out."

GHB, which can be fatal when mixed with alcohol, is particularly dangerous in the culture of excess that is the Ibiza experience.

'Market experiment'

Dr Francisco Mueles, in charge of casualty at the Can Misses hospital in Ibiza town, told 4x4 the liquid form of ecstasy was at the centre of a new and dangerous holiday phenomenon.

"It worries us a lot because we don't understand how the drug works and much less so when it's taken with other toxic substances like alcohol and cocaine."

Easily made from industrial solvent and dissolved in water, GHB has claimed twelve lives in Britain, where the Home Office intends to ban it by the end of 2002.

Dr Francisco Mueles: The body count will rise

Ibiza DJ Lenny Krarup said some holidaymakers had already witnessed the drug's potential damage, earning it the nickname 'GBH'.

"Two years ago there was an incident where GHB was used to spike the drinks of a number of people who all collapsed in epileptic fits.

"Two went into a coma and one died. It happens repeatedly but there is a lot we don't hear about."

Medics say although most people recover from the comas, GHB poses long term risks for the young people tempted to take it.

Dr Mueles said: "It raises a series of questions about brain damage in the long term. It's an experiment by the market.

"This a very dangerous drug and the market will soon discover that when the body count begins to rise."

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4x4 Reports: Dark side of the sun was broadcast on BBC 1 on Monday 5 August at 1930 BST.