A quarter of a million Britons risked seven-year jail terms last month to buy ecstasy from dealers who could face life in prison. That’s what the law says, anyway. Since 1977, the Home Office has categorised MDMA as a class A illegal drug, reflecting an official line that says ecstasy is among the most dangerous substances on the street. From crown court judges to loved-up ravers, almost no-one believes this to be the case; in practice, the justice system has long since ceased to approach ecstasy in the same way as heroin or crack cocaine. But as home secretary Jacqui Smith resists fresh calls for the drug’s declassification, it’s clear that the present government has no intention of allowing mere facts and practicalities to get in the way of its ostentatiously tough stance on drugs.

Britain’s tripartite drug classification system was intended to be a guide for legal authorities and potential users as to the relative danger presented by street drugs. For all the paranoid suspicions that Westminster’s chief goal is to stop the nation’s youth having a good time, illegal drugs are criminalised on the basis of harm – both to users and to those around them.

The UK model is based on an enticingly simple principle: the greater the potential for harm, the higher the class. And there’s the rub - ecstasy simply isn’t that harmful. People can die from MDMA use, whatever aficionados might tell you: 30 in Britain each year, according to one estimate. But the overall impact of ecstasy pales in comparison with other drugs. This was made shatteringly clear by a Lancet study last year by a team from the Academy of Medical Sciences, which examined various social and biological factors to establish the relative dangers of the most popular drugs. Ecstasy was the least harmful of all the illegal substances studied, well behind class C-graded cannabis and ketamine, as well as alcohol and tobacco. Class A stablemates heroin and cocaine were out of sight. The drug classification system, concluded the experts, is “not fit for purpose."

Try telling that to the Home Office spokesman who last month dismissed renewed calls for a rethink on ecstasy with the sensational assertion that “ecstasy can and does kill unpredictably." All sorts of things kill unpredictably, as anyone who has died putting on his trousers would love to come back and tell you. It’s the predictable killers that should be the chief object of the government’s attentions–the drugs, like heroin, that have been shown to leave a trail of shattered lives wherever they gain a foothold. The classification model offers a means of ranking more than 500 controlled substances according to the damage they cause. For a prominent drug to be so manifestly out of place renders the entire system all but unusable.

How are we to explain the government’s intransigence? The endlessly antagonistic tabloid press must take its share of the blame, having set up the parasitic junkie as a kind of pantomime villain, a menace to be resisted at all costs. “To give low-lifes a daily fix of an illegal substance seems like a bad taste joke,” howled the Daily Star last year, after a police chief suggested that NHS provision of heroin could slash crime rates. No matter what the common sense content, all drug legislation will be portrayed as being either hard or soft on drugs; and the latter simply is not a vote-winner.

All recent discourse on this subject must be seen through this lens. When David Cameron last week dropped his support for ecstasy declassification, it served slightly to relieve the suspicions raised by his refusal to say whether he has used cocaine. A similar populist logic lies behind Gordon Brown’s insistence that cannabis should be re-established as a class B substance, despite overwhelming evidence to the contrary. But this is a bullet that has to be bitten. A functioning classification system is a vital weapon in the fight against harmful street drugs – not a political football.