Three types of chemical highs which are currently legal are due to be banned by the end of the year:

GBL (Gamma-Butyrolactone) is a chemical solvent which is converted in the stomach into the Class C drug GHB (gamma-hydroxybutyrate) which is nicknamed "liquid ecstasy".

GHB emerged on the party scene in the 1990s and was banned in 2003.

GBL has already been banned for personal use in several countries including the United States, Canada and Sweden but its industrial use as a paint stripper means it is widely available on the internet and even in some health food shops for reportedly as little as 50p per dose.

The UK's Advisory Council on the Misuse of Drugs highlighted last August that the "harms and misuse" of GBL were commensurate with a Class C drug.

The dangers were also highlighted in a report by the European Monitoring Centre for Drugs and Drug Addiction earlier this year.

It said GBL was becoming more popular as a recreational drug and, despite security measures to limit its use in clubs and pubs, it was regularly being smuggled into London nightspots mixed with water in plastic bottles, condoms and balloons. It is virtually tasteless when diluted.

The report said: "The ease with which GBL and thus GHB can be acquired allows potentially much easier and cheaper access than that usually found in illicit drug markets in the EU."

It said people who bought the drug ranged from clubbers seeking euphoria to people interested in purported anti-ageing remedies or seeking increased sexual function.

The death of student Hester Stewart, 21, in April this year prompted calls for GBL to be outlawed which were led by her family.

Miss Stewart, a cheerleader with the Brighton and Sussex Waves, died after she consumed GBL with her on-off boyfriend Anthony Morrison after returning to his shared house in Brighton following an American football awards ceremony.

Mr Morrison said it was the first time that Ms Stewart, a University of Sussex student studying molecular medicine, had taken the drug, which had been bought online from a site which warned it was not for human consumption.

She was dead when he woke up at 9am on April 6, he told an inquest into her death.

The inquest was told although the level of GBL consumed by Ms Stewart was low and would have led to full recovery in some people, its combination with alcohol proved fatal.

Brighton and Hove coroner Veronica Hamilton-Deeley, who recorded a verdict of misadventure, said people using drugs like GBL recreationally needed to understand they were playing "Russian Roulette".

The Home Office plans to classify GBL as a Class C drug and ban it when intended for human consumption.

Synthetic cannabinoids, like the brand Spice, will become a Class B drug, the same as cannabis.

The Government's drug adviser called for Spice to be banned earlier this month, saying it was created using dangerous chemicals although sold as a "natural" high.

Professor David Nutt, chairman of the Advisory Council on the Misuse of Drugs (ACMD), said: "Spice and other synthetic cannabinoid products are being sold legally as harmless 'herbal legal highs'.

"However, the herbal content is coated in one or more dangerous chemical compounds that mimic the effects of cannabis.

"These are not harmless herbal alternatives and have been found to cause paranoia and panic attacks."

Pouches of the drug are currently widely available on the internet and in so-called "head shops" for around £20 for three grams. It is sold under brands such as Spice Silver, Spice Gold, Spice Diamond and Spice Yucatan Fire.

The drug was banned in Germany, Austria and France, earlier this year. Reports from Germany suggested some users suffered heart problems after smoking the drug.

Spice and other so-called synthetic cannabinoids escape existing UK drugs laws because they do not contain marijuana and are not chemically related to it.

But by spraying synthetic additives on to herbs, dealers can create similar intoxication in users to that caused by THC, the active ingredient in cannabis.

Analysis of samples of Spice showed it had a "higher potency" than THC, the ACMD warned.

Its report said herbs listed on the packets of the drug were often not found inside and large amounts of Vitamin E were used to hide other chemicals.

It said users could not "assume the same effects from the same product the next time they use it".

BZP (Benzylpiperazine) is used to worm animals and as a fertiliser but has become popular for recreational use as it can have a similar effect to amphetamine.

The drug is said to create euphoria and enhance a user's sense of taste, sound and colour.

Some websites have marketed it as legal ecstasy and sell it for as little as £1 a tablet but it has already been banned in countries including America, Australia and Japan.

Assistant deputy Sheffield coroner David Urpeth described BZP as a "huge concern for society" when he recorded a verdict of misadventure into the death of Daniel Backhouse, 22, from Sheffield, who suffered heart failure after mixing BZP with MDMA, the powdered form of Ecstasy.

Mr Urpeth, speaking in May, said there was a "significant chance" of more deaths where BZP was mixed with ecstasy.

The Government plans to control BZP, and related piperazines, as Class C drugs.