This year marks an unfortunate anniversary. It is 100 years since the first international treaty to control narcotics was signed in The Hague, launching a war on drugs that has ripped apart nations, killed thousands of innocent people and earned billions for the most vicious gangsters on earth.

The one thing the century-long conflict has failed to do is stop people taking drugs. Perhaps this is unsurprising, since the original legislation was really driven by anti-Chinese hysteria rather than public health concerns. Then the fight was ramped up by President Nixon, in search of new enemies after rising to prominence fighting communism.

Yet still our myopic leaders engage in a self-defeating struggle to stem the flow of drugs. They talk hypocritically about harm reduction as murder rates soar in countries caught in the crossfire and gangs strike fear into inner-city ghettos. And they ignore evidence of prohibition’s failure that piles up almost as quickly as the bodies of victims.

For a government that believes in the market, falling street prices should demonstrate the futility of their stance. No such joy. But at least we can be grateful the posturing of politicians hooked on failed policies is being exposed by harsh reality.

Yesterday we saw the latest example, when police chiefs pointed out that government attempts to ban “legal highs” are doomed to failure. In leaked evidence to the Home Affairs Select Committee, the Association of Chief Police Officers highlighted the nonsense of constantly adding to the list of banned substances, especially given the speed with which the market creates replacements.

In addition they questioned the use of legislation to tackle drug taking, insisting they would focus precious resources on serious crooks while taking “a less robust enforcement approach” to young pleasure-seekers. They are right to do so.

There are many arguments against prohibition: the £200 billion-a-year global trade fuels crime, corrodes society, destroys communities, inflames racial tensions, wastes huge sums on ineffective enforcement and even damages, rather than protects, public health. You would have to be stoned to think banning drugs does the slightest good.

Ministers know such policies do not work. Seven years ago, a confidential strategy paper drawn up for Tony Blair’s Cabinet admitted law enforcement agencies were stopping less than 20 per cent of cocaine and heroin — and that they would need to seize four times that to make the industry unprofitable.

Yet still they sit like Canute as the tide of narcotics washes around them, inflicting most pain on the poorest communities. Illegality serves only to drive up prices, the massive margins ensuring chaos follows in their wake. Now a series of sobering studies have emerged that undermine their case still further.

Take what happened after the clubbing drug mephedrone was banned two years ago. The move led to the seventh resignation of a member of the Government’s advisory council in six months, highlighting how politicians ignore scientific evidence on this issue.

A report in the Journal of Substance Use last month by researchers at Guy’s and St Thomas’ NHS Foundation Trust and Lancaster University showed how the ban backfired. Their survey of south London clubs found purity fell after the law change but prices rose; despite this, mephedrone’s popularity appeared to have soared after it was outlawed.

Contrast this with cannabis. Cycling around London, I regularly catch the smell of the drug being smoked by people sauntering along the street. And as any visitor to Camden Market discovers, there is a booming market in cannabis cultivation, forcing the Government to advise courts to show greater leniency to domestic growers.

As The Economist noted recently, the drug has been effectively decriminalised on the sly. But instead of leading to an upsurge in reefer madness, this liberalisation has been accompanied by the fastest fall in Europe in the proportion of people admitting use of the drug — down from 10.9 per cent to 6.8 per cent of adults in just under a decade.

This is unsurprising. Several European countries have made moves towards drug decriminalisation, most notably Portugal, which made possession a civil offence. Last year, an inquiry found cannabis and cocaine use had fallen over the following decade, while heroin use remained above average in the rest of the continent.

The interesting thing is what did not happen. Junkies did not flock there, nor did gangsters. But while another million people in Britain have gained criminal records, wasting police time and clogging up the courts, thousands of Portuguese users have become supervised patients in the health system.

Or look at the Czech Republic, which decriminalised drugs for personal use, then made them illegal, then decriminalised them. A huge study into this near-perfect experiment published at the end of last year found none of the key arguments for prohibition stood up — but the country frittered away a fortune.

Little wonder the Czech prime minister last month joined those Latin American leaders fed up with seeing their countries wrecked urging the UN to adopt a new approach to drugs based on prevention and treatment rather than prohibition.

If only our own political masters showed such courage. Instead, they are fighting their foolish war. It is one more reason for the disconnect between Westminster and the rest of the country: politicians who use and tax the lethal drug alcohol, cause of so many health and social problems, then binge on laws to lock up those who prefer less damaging stimulants.

We are led by a generation of politicians young enough to know better. Indeed, in one more measure of hypocrisy, many have used drugs themselves — just like many journalists on those papers demanding ever-tougher sanctions.

There is no need to cower behind the pusillanimous politics of prohibition. Listen to Bob Ainsworth, whose experiences as a Home Office minister turned him into the unlikeliest of drug campaigners: as he says, the public is far more progressive than politicians and sections of the press on this issue.

After 100 years of failure, it is time to be brave, take a deep breath — and declare peace in the ill-fated war on drugs.