ANYBODY walking into the Shiva Headshop, in the east London suburb of Greenwich, could be forgiven for thinking that drugs are legal in Britain. In the centre of the store, a glass case displays expensive stainless steel vaporisers. There is a vast array of cannabis-themed grinders, bongs, pipes and ashtrays. As your correspondent enters the store, some adolescents wander out, one clutching a discreetly wrapped foil packet. Hanging behind the counter, stacks of these are on offer, with names like “Blessed” and “Iced Diamonds”. On the shop’s website, they promise to “keep you humming all night”.

So-called “legal highs”—so novel and fast-evolving that they are not controlled under the Misuse of Drugs Act—are reopening the drugs debate. On January 14th the All-Party Parliamentary Group on Drug Policy Reform called for an overhaul of Britain’s relatively stringent drugs laws, proposing that “less harmful” new substances be regulated and sold in chemists. In December the Home Affairs Committee called on the government to set up a royal commission to consider decriminalising or even legalising certain drugs. Overwhelmed by the number of new substances and worried about their effects on users, some police chiefs and doctors have also recommended change.

The government dismisses all such suggestions. “We have a policy that actually is working,” claimed David Cameron, the prime minister, in December. Data from the Crime Survey of England and Wales seem to back him up. The use of conventional drugs such as cannabis, cocaine and ecstasy is declining in Britain, particularly among the young. The number of 18- to 24-year-olds registering for treatment for heroin addiction has fallen to its lowest level since records began in 2001.

But this may have little to do with legal controls. Alcohol consumption is also falling even though the law has not changed. Cannabis use actually fell after the drug was reclassified as less harmful in 2004. And, as the shop in Greenwich shows, many new substances are filling the gap. Drugs like heroin and cannabis are “yesterday’s news”, says a drugs officer in the West Midlands Police. Instead of waiting on street corners for an unreliable dealer to arrive, many young drug users are simply ordering their supplies online.

Under a law introduced in 2011, new psychoactive substances can be banned temporarily, before being fully criminalised after a year. But the police are “flat-footed” trying to keep up with the pace of change, says Tim Hollis, the drugs spokesman for the Association of Chief Police Officers. New drugs pop up so frequently that sniffer dogs must undergo retraining every few weeks to learn the new scents. Even the suppliers struggle: lots of drugs sold as “legal highs” turn out to be banned.

It is not clear that bans reduce availability or greatly deter consumers. According to Fiona Measham, who researches drug-taking and drinking habits at the University of Durham, mephedrone, which was banned in 2010, is now a staple of the clubbing scene: it is typically taken alongside ecstasy and cocaine. Police officers report that gangs have violently muscled in on the distribution of the drug, which is now cut with the same harmful chemicals as cocaine. Its use has become more damaging: mephedrone is now injected by some users as often as five or six times a day. Ketamine, a similar drug which was controlled in 2005, is now causing many users severe health problems, such as bladder damage.

Liberalisation would reduce some of these side effects, argues Molly Meacher, a peer on the all-party parliamentary group, and help to divert drug users to the least harmful substances. But the government’s reticence is understandable. Though experts demand change, there seems to be little public appetite for drugs to be more openly available. According to data from the British Social Attitudes Survey, British people’s views on cannabis have hardened since 2001. Then just 46% of people thought that the weed should remain illegal; now 63% do. But perhaps ministers should have some courage. As one MP said in 2002, going to war on drugs “does not work”. His name was David Cameron.