In 2009, ecstasy, the drug that had sparked a cultural revolution in Britain two decades beforehand, was on its knees. That year, forensic scientists found that over half of ecstasy pills seized by police contained no MDMA at all. They were duds packed with a mixture of caffeine and underwhelming stimulants such as BZP and cheap speed. As a product it had become defunct. By 2012 ecstasy use, as with many other drugs, was falling. There was talk of a nation falling out of love with getting high.

Yet all of a sudden, ecstasy is back and in demand by a new generation. Latest figures from the Home Office’s annual drug survey published yesterday reveal a surge of ecstasy use among young people. Use among 16- to 24-year-olds has nearly doubled over the last two years to levels not seen since 2003, when newspapers were warning that Britain was facing an “ecstasy epidemic”.

In an era when teenage drug use is supposedly dominated by an alphabet soup of new psychoactive substances, or “legal highs”, why is this happening? The biggest factor is purity. More people are taking it because it’s got more MDMA in it. Ecstasy was so poor between 2008 and 2012 because the global MDMA market was shattered by a series of huge seizures of the chemical used to make the drug, safrole oil. One haul resulted in the destruction of 33 tonnes of chemicals that would have made enough ecstasy pills to supply the entire UK market for five years.

But wily Dutch criminal chemists who manufacture the bulk of Europe’s ecstasy found a new way of synthesising MDMA, using a chemical called PMK-glycidate, a legal substance easily available and relatively cheap to order in bulk from underground Chinese chemical labs. As a result, ecstasy in most of western Europe now has MDMA purity levels reminiscent of the early days of the rave era in the late 1980s. Analysis of drugs at festivals and clubs this summer, carried out by Fiona Measham, a professor of criminology at Durham University, found crystalline ecstasy that was over 90% pure.

Like few other drugs, ecstasy use is, in a charming kind of way, highly infectious, because it is a group experience

A new breed of super-strong ecstasy pills, far more potent than the pills that were being popped at the height of the rave era in the 1990s, are widely available. Tests on UPS branded pills manufactured in Holland, which hospitalised six young people in a Middlesbrough nightclub in February, found they contained 278mg of MDMA, 10 times stronger than the average ecstasy tablet on sale five years ago. Yet this pure MDMA would not have sparked such a spike in popularity without the appropriate setting in which to take it.

The Warehouse Project in Manchester, for instance, is in essence a colossal student rave. It is no coincidence that its club nights start in September, when the student loans arrive. Over one weekend, at £25 a ticket for Friday and Saturday nights, the 2,500-capacity venue pulls in £125,000. It’s big business.

And a significant proportion of these customers are young people who take ecstasy, a reality that the owner of the Warehouse Project has tried to tackle, by inviting Measham to run an on-site ecstasy testing facility at his club in order to alert customers about the potency of the drugs.

Like few other drugs, ecstasy use is, in a charming kind of way, highly infectious, because it is a group experience. “If a club is on ecstasy people want to be part of that vibe, they don’t want to be sat in the corner scowling on cocaine. So they will join in,” says Measham.

For this new generation of young clubbers, the mainstreaming of rave culture with huge electronic dance music (EDM) events in America, itself borrowed from the UK, is likely to have boomeranged back here. It’s a scene intrinsically linked to MDMA, or as the Americans call it “Molly”, a fact constantly broadcast in songs and interviews by pop stars such as Miley Cyrus to their teenage fans.

Many people are unaware that the average finger-dab of crystal MDMA is the equivalent of one pill, says Measham. This summer she saw drug users at festivals swallow huge crystals of MDMA rather than grind it up. Dab doses go up, she says, when people share bags because of what she calls “competitive dabbing”.

And the longer the fingernails, the more powder can be scooped up. Because of this, she started a campaign called Crush, Dab, Wait, designed to teach young people how to use ecstasy more safely.

The return of ecstasy – alongside a second consecutive year of rising drug use among young people, including LSD, cocaine and magic mushrooms – should send a shiver up David Cameron’s spine. It was he who in 2012 rejected calls to set up a royal commission to re-evaluate our creaking drug policy on the basis that drug use was simply going out of fashion. The mantra was, drug use is falling, so our policy must be the best. As I warned him in 2012, it was a stance based on a shaky premise, open to the whims of notoriously unpredictable drug trends.

With more young drug users taking higher purity ecstasy, the risk of overdose rises. Now drug use is going up, and the risks are multiplied, it will be interesting to see what, if anything, the government will do about it.