Clubbers are unaware of the potential dangers of mixing an increasingly popular drug with alcohol, say drug campaigners.

The use of gamma hydroxybutyrate, also called liquid ecstasy, and nicknamed "GBH", has started to increase on the club scene in recent months.

It is popular because it is relatively cheap, and is not illegal to possess.

However, overdoses are common - using the drug can even lead to convulsions and coma.

This is because the difference between a "safe" dose and an overdose is tiny.

And scientists warn that mixing the liquid into alcoholic drinks could produce a deadly cocktail, as this accentuates this effect.

And there are fears that it is becoming a drug of choice for date rapists, who use it to sedate their victims so they can be attacked.

It is ideal for this purposes as it comes as a colourless, odourless liquid that is easy to slip into drinks.

Last month Scotland Yard detectives appealed on the BBC's Crimewatch programme after a woman was raped in London after her drink was apparently spiked with the drug.

Festival season

A leading UK drugs charity, Turning Point, said that it was not aware of any deaths among GBH users in this country, but that given the increase, it was only a matter of time.

A spokesman said: "The drug has been around for a while, mainly used in the gay club scene.

"It produces a feeling of euphoria - but It can be fatal if mixed with alcohol." Another drugs charity is urgently producing an advice leaflet to distribute before the summer outdoor festival season.

"GBH" is freely available, over the internet, through mail-order catalogues and in sex shops.

It is a colourless liquid normally sold in small bottles.

It was originally used by bodybuilders to stimulate muscle growth, but emerged on the gay scene in the early 1990s.

Now two cities in the North of England, Leeds and Manchester, are reporting major problems with the drug, including clubgoers suffering serious side-effects after taking it.

The club scene in Leeds, in particular, is said to be "saturated" with the drug.