Ask them at the right time of day and most ravers will tell you they'd rather not be criminals. Some of them might feel compelled to take ecstasy, which remains a Class A drug in Britain, by the illegality that accompanies it. But most – and this is especially true of regular and recreational users – think it absurd that their pursuit of pleasure be deemed illegal. In their view, the harm associated with it mostly affects those who "drop" the pills themselves, and is therefore not the business of Government.

In this regard, most users of ecstasy inhabit a tradition whose pioneers include Keith Richards. "I've never had a problem with drugs," the Rolling Stone said. "I've had problems with the police." And it's precisely the ubiquity of this view that has caused a relatively new pharmaceutical industry to blossom.

You don't have to be a member of the flower power generation to see that "legal highs" might carry the whiff of oxymoron. The term refers to a commonly available breed of drug that replicates the effects of ecstasy but carries none of its criminality.

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At least not for now. Before leaving the post of Home Secretary, Jacqui Smith said last month that she was considering taking the prefix out of "legal highs", and just sticking with the "high" bit. "It's absolutely right that we continue to adapt our drug policy to the changing environment of substance misuse," Smith said, following the death of a Sussex University medical student named Hester Stewart. The 21-year-old's body was found near a container of GBL, a "legal high" also known as paint stripper. Smith didn't have time to implement the plans, but they sit close to the top of her successor Alan Johnson's in-tray.

These "legal highs" are distinguished from ecstasy by their content rather than their effects. Ecstasy, which generally comes in the form of pills – also known as "disco biscuits", "beans", or "party poppers" – is essentially made of methylenedioxymethamphetamine, or MDMA for short (hence the nickname "Mandy", sister of cocaine "Charlie"). Users of ecstasy generally prefer to swallow MDMA in its purer form, as a crushed-up pink or brown crystal, rather than in pills bought from dealers, where other alien powders such as bicarbonate of soda (which helps cakes to get high, but not humans) might be added. In this sense, the commonly consumed form of ecstasy can be thought of as MDMA plus any junk the dealer wants to throw in. The more junk there is, the better his margins and the worse the pill.

The drug causes the release of serotonin, a neurotransmitter, and stimulates feelings of intimacy and ecstasy, while reducing inhibitions. It also stimulates the release of dopamine and noradrenaline, also neurotransmitters, and oxytocin, the so-called love hormone associated with orgasm and childbirth. By making the heart beat faster, ecstasy pills cause users to experience a period when they are "coming up", feeling a surge. Once the effects have fully kicked in, they attain a sensation described in common parlance as "rushing" or "buzzing".

"Legal highs" do much the same thing. There are two common forms, both of which Jacqui Smith had within her sights. The first is GBL (gamma-butyrolactone), an industrial solvent also used as a paint stripper (seriously) and sometimes confusingly referred to as liquid ecstasy – which is misleading, because there are types of liquid ecstasy that are in fact illegal. It is a fast-acting drug with vaguely hypnotic and euphoric effects that are accentuated when mixed with alcohol.

The second major type of legal high is BZP (benzylpiperazine, sometimes called "Benny"), whose effects on the brain are very similar to MDMA. BZP began life as a worming treatment for cattle, but the likeness between it and ecstasy has led to a surge in popularity. A recent report for the European monitoring centre for drugs and drug addiction highlighted several side effects – stomach pains lasting 24 hours, headaches, nausea, vomiting – but received very limited media coverage in Britain.

A few years ago a craze began for another type of legal high, piperazines, which are from the same class as Viagra but have similar effects to ecstasy. But those drugs, marketed as PEP pills, have faded in popularity.

Purely in order to serve the interests of these pages, your correspondent was convinced to purchase and consume two "legal highs". This he did on the River Cam in Cambridge two weekends ago, a ripe location if ever there was one for such indulgence. The pills can be procured from, among others, shivaheadshop.co.uk. The website advertises bongs, vaporizers, pipes, chillums – and legal highs and incense.

Within the final category there is a huge range, including herbal blends, incense sticks, Koru energy strips, natural herbal remedies, snow blow, party pills, Jungle High energy pills, and Happy Caps. This newspaper obtained some Blessed party pills (four of them at £12.99) and a box of Happy Caps (five at £5.99). Together with shipping costs of £2.45, the pills arrive in three days at a total cost of £21.43. You can pay by card, which is not a method of reimbursement your average dealer is familiar with. Most dealers will charge between £3 and £4 for a pill, so though the Happy Caps represent very good value, the Blessed party pills are about an average price.

The Blessed pills don't achieve the aim promised on their package – "seeing the light" – because within 20 minutes of consuming one on a full stomach your vision begins to blur. At first, this happens slowly and gradually, and then much faster. It's not a case of losing your sight altogether – people are still distinguishable – but there is certainly a generalised haziness. With it comes an overwhelming sense of happiness, together with a strong affection for those in your company. This mellow buzz lasts, on one pill, for around three and a half hours, peaking during the second hour. Even after the buzz has gone, it takes a few hours of sleep before you return to a proper sense of sobriety.

The effect of the Happy Cap pills is milder (as the price would make you expect) and there seemed a stronger short-term memory loss. The buzz lasts for an hour or so less than with the Blessed, but there is basically the same all-pervading sense of excitement and jollity.

It would be remiss not to mention a slight come-down the following morning, when the serotonin levels in the brain are grasping their way back to normal. Regular users become accustomed to this, knowing it will go away, but to new users they can be a nasty shock.

Why this is experience is legal, while consumption of MDMA is not, cannot be comprehended without abandoning rationality. The former Home Secretary might have a point about consistency. No figures exist for how many "legal highs" are taken each weekend, but police now consider them a growing concern.

The true extent of ecstasy consumption is only now becoming clear. It was helped 18 months ago by the curious tale of Mr A, a patient formerly under the care of the addiction centre at St George's medical school in Tooting, south London. Between the ages of 21 and 30, this chap consumed 40,000 ecstasy pills. He started with five over a weekend, migrated to 100 each month, and finished with 25 a day, a habit he sustained over four years. Doctors were not surprised to discover a causal link between this behaviour and the hallucinations, paranoia, muscle rigidity and short-term memory loss that this man endured.

But when Richard Brunstrom, the Chief Constable of North Wales Police, had the audacity to claim that ecstasy was a "remarkably safe drug" (try taking 25 ibuprofen a day for that long – actually, don't), he was lambasted as a dangerous naïf. Similarly, a distinguished government drugs adviser, Professor David Nutt, whipped up a media storm when he said in a journal article that taking ecstasy was safer than riding a horse.

Why would these public figures say such things? Figures from 2003 (among the latest available) estimated there are 730,000 users of ecstasy in the UK, taking between 500,000 and two million pills each weekend. Since 1994 there have been approximately 400 deaths involving ecstasy – including, of course, that of Leah Betts in 1995. But around a hundred people die each year from adverse reactions to, or overdoses of, aspirin and paracetamol.

It has long been a staple of the case made by those in favour of legalising ecstasy that its use is so widespread as to make the law an ass. The advent of "legal highs", and their booming availability, now proves that point indubitably.

Party drugs: What's allowed

* Although GBL, an industrial solvent, can be bought legally, the body converts it into GHB, a common "date rape" drug, which is banned in the UK as a Class C substance.

* BZP or "Benny" originated as a worming treatment for cattle. Its effects are similar to those of ecstasy, a Class A drug.

* Other legal highs include Blessed party pills and Happy Caps, containing ingredients such as caffeine, kola nut, clary sage and geranium.

* Magic mushrooms, which have hallucinogenic qualities, were legal until 2005, when they were reclassified as Class A (except in their fresh form).

* Class A drugs include ecstasy, heroin, LSD, crack, magic mushrooms, cocaine and amphetamines.

* Possession of a Class A drug currently carries a sentence of up to seven years in prison or an unlimited fine.

Fiona Roberts

Should drug laws be tightened to include legal highs? Or should rules on all drugs be relaxed? Write to: yourstory@independent.co.uk