Their thoughtful and well-researched report, which argues that Western efforts at eradication are decades away from success, is the best attempt yet to shed light on this murky economy, whose embrace stretches from militant terrorism to the heroin on British streets.

There are now between 25 and 30 key traffickers, the majority based in southern Afghanistan, “working closely with sponsors in top government and political positions”, says the report, which is based on extensive local interviews by staff of the UN Office on Drugs and Crime and the World Bank. However, all is not entirely gloomy. The rest of the economy is growing strongly: government control of the country has improved; and some areas cleared of drugs have stayed that way.

Afghanistan’s opium economy was between £1.3 billion and £1.4 billion in the past two years, the report says — equal to 36 per cent of the legal, non-drug economy in 2005-06. But the opium business has remained roughly the same size, while the rest is growing.

You might ask whether in some sense the trade is helpful for Afghanistan. After all, the country does not have many things that it is good at, and growing opium does inject cash into the economy.

The authors, who consider this seriously, conclude all the same that it contributes to a damaging “Dutch disease”, as economists put it. Traffickers save the proceeds or spend them on imports, which pushes up costs and the exchange rate, making the legitimate economy less competitive.

Understandably, most attention has focused on the political damage of the illegal trade. The report is not the first to describe how it has fostered corruption, as farmers pay police or officials not to have crops wiped out. However, it is more original and detailed in analysing the causes. The best section, The political transition and the evolution of organised crime, argues that it is out of date, by three years, to think of “a stable Kabul, governed by a beleaguered central government, encircled by a lawless periphery dominated by voracious warlords”.

Instead, much trafficking has moved into the hands of organised crime, it says, beginning in 2003. Corruption in the Ministry of Defence meant that payments intended to secure the loyalty of warlords were stolen. “The total amount to be provided to the (armed) groups” from the government budget was £50 million, but about 60 per cent was diverted within Kabul itself.

That weakened control over armed groups and encouraged them to develop links with criminals. Political leaders are now keen to distance themselves in public from traffickers, the report says, but “it remains impossible to operate in the criminal underworld without support . . . from the political ‘upperworld’ ”.

The report also notes that “elements in the Ministry of Interior” have become deeply involved in organising protection for criminal rackets and in appointing tolerant police.

Nor is the report encouraging about the record of eradication programmes, now led by Britain. It argues that the effects have been patchy or counterproductive, felt most by the poorest, while consolidating the trade in the hands of “fewer, more powerful, politically connected” barons.

What should Kabul and other countries do now? Despite a fondness for management consultant vocabulary, the report comes up with sensible suggestions. Efforts should be concentrated in areas where farmers have good access to land and water, and so could grow something else; experience shows that that is where success is greatest.

It recommends focusing enforcement on areas that have not yet become dependent on drugs (and notes that opium still takes up only 3 per cent of farmland). The authors also urge agencies to anticipate the inevitable, painful effects of a successful crackdown, such as soaring rural poverty and the indebtedness of those who were relying on future drug income.

Most urgent, they say, is the need to rip the trade out of the police and Interior Ministry before it has become more entrenched.

They are indisputably right that this effort will take decades, even if it works. But the volume and detail of their interviews show, as they put it, that “it is possible to look into the ‘black box’ ” of Afghanistan’s drug industry. That is a good start.

Afghanistan’s Drug Industry www.unodc.org

6,100

Tonnes of opium produced this year, enough for 610 tonnes of heroin

Source:World Bank/UN report

Times Recommends

• A new kind of western conservatism
• Georgiana is the wrong role model
• Alaska, where cops don't bother you