New warnings are being issued about the date-rape drug GHB - known as liquid ecstasy - after a report suggested nightclubs are seeing a massive increase in its use.

The colourless, odourless drug, has been linked to date-rape cases where women have been sedated before being sexually assaulted.

News of the increase in the drug's use in UK clubs has been broken by the charity Release, which describes the substance as "more dangerous than ecstasy".

A campaign has been launched to ban the drug, which is sold over the internet, through mail-order catalogues and in sex shops.

Release says it is concerned to inform clubbers about the effects of its use and the dangers of overdoses and is sending out leaflets to clubs and drug agencies across the UK in time for the summer season of music festivals.

Convulsions and coma

A few drops of gamma hydroxybutate (GHB) slipped into a drink can cause unconsciousness within 20 minutes and victims will often have no memory of what has happened.

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, nicknamed GBH.

Used by bodybuilders to stimulate muscle growth, the drug emerged on the gay scene in the early 1990s.

In recent months, it has slipped into mainstream club culture and is now said to be a considerable problem in a number of cities, particularly Leeds and Manchester.

In February, US President Bill Clinton signed a law banning GHB - which was linked to more than 60 deaths in the US since 1990 - and placing it in the same category as heroin and cocaine.

But although the drug is potentially lethal when taken with alcohol, it is legal to possess in the UK and easy to make.

It is normally sold in bottles as a colourless liquid. But overdoses are common and can lead to convulsions and coma.