It's hard to imagine a policy as comprehensive in its failure, as overwhelmingly counterproductive, as the war on drugs. Tom Feiling has the statistics. In the last 35 years, the US has spent $500bn attempting to reduce the availability and purity, and increase the price, of illicit drugs. Yet cocaine purity is up, the drug is as available as it ever was and its price dropped 50% in the decade up to 2003. Cocaine, formerly the preserve of the super-rich, has become democratised. The result has been an explosion in demand and a corresponding explosion in supply. Nothing, it seems, can stop the flow.

Worse than the failure of attempts to destroy the cocaine industry, however, are the side effects. Thousands of hectares of rainforest have been wiped out by aerial spraying; drug-financed corruption has infiltrated the governments of Latin America and the Caribbean; inner cities have been decimated and hundreds of thousands of people pointlessly incarcerated. Then there is the violence: assassinations, drive-by shootings, human rights abuses. "Cocaine has paid for everyone to enjoy the fruits of violence," Feiling writes.

It's no great secret that prohibition hasn't worked. What's so depressing about the war on drugs is not that we haven't won it, nor even that it cannot be won, but that there appears to be no way out. "What to do", asks Feiling, "but continue as before?"

Feiling wastes no time on high-rollers or perforated-nostrilled celebrities. He is interested in the whys and hows of the trade. Everything cocaine touches turns to lead. How it came to this is the question he explores in this extensively researched, passionately argued book. "I wanted to hear from those who work day-to-day on the cocaine trade routes," he writes, "to bring into the open those tight-lipped mechanics of the cocaine trade." The routes in question are the major supply lines: Colombia, Mexico and Jamaica. He interviews the consumers, the traders and the producers, as well as the law enforcers. The results are sometimes startling.

"I hope to puncture some . . . stereotypes," he says in the introduction, before launching an assault on wrong-headed policies and the buffoons responsible for the whole sorry state of affairs. And what a lot of them there are! The peddlers of drug panics ("irrational, hysterical and moralising"), narcotics policing techniques ("brutal, corrupt, racist and ineffective") and, especially, the legislators behind it all, with their "gnat-like attention span and general indifference to the consequences of their actions". Anyone who strays into his line of fire gets both barrels. Feiling is scathing about the "nosiness, envy and sanctimony that masquerades as the 'public interest'" and "the ritual inflation and deflation of mediocrity that passes for 'celebrity news'". Journalists get some flak, too, for "glibly" reporting statistics that turn out to be incorrect.

Feiling writes well, sometimes extremely well. Parts of this book reminded me of Roberto Saviano's Gomorrah. The account of crack is strong, the chapter on legalisation very good indeed. He has traced and interviewed the right people and asked the right questions. The problem of cocaine is complex, and demands a complex examination. It gets one here. This is a serious book, raising serious issues, for serious readers. The author's encyclopaedic knowledge, however, has its downside. As he jumps from one issue to another, from one country to another, it's easy to get lost: at times I found myself feeling battered by the sheer weight of detail. Also, some of Feiling's generalisations seem a little too neat. He asserts that the CIA "approved and supported" cocaine smuggling by the Contras; that, according to the domino theory, "every third world nation that aspired to some measure of autonomy was to be forced into submission before they fell to Soviet expansionism". While there is some truth in both assertions, I'm not sure they're entirely accurate as they stand.

What matters, however, is whether he is successful in making his case: that prohibition is "unworkable and counterproductive". I believe he is. Recent news reports from Argentina and Mexico indicate that their governments may be coming to the same conclusion: legalisation must, surely, be a less damaging route.

Admittedly, for those American legislators who see legalisation as an unconscionable commie plot, there are alternatives. How about solving the problem of inner-city poverty, providing proper healthcare, tightening control on guns, mending the economies of the producer countries and excising corruption from Latin America? "Compared to such utopian prospects, the legalisation of drugs looks like a pragmatic response to a multi-faceted problem that has outlived all the solutions that have been tried to date."

The book ends with a warning. "Unless there is a fundamental reassessment of the problem and a willingness to consider hard solutions, prohibition can only make for bigger problems in the future." He's absolutely right there.

Dominic Streatfeild's Cocaine: An Unauthorised Biography is published by Virgin.