Cheap heroin is beginning to appear on Britain's streets just a few months after a record crop of opium poppies was harvested under the noses of the UK's beleaguered garrison in Afghanistan. The sticky resin scraped into packages by the farmers in Helmand sells for £55 a kilo at source. At the user end of the chain it can fetch up to £100 a gramme - but the glut available now means street prices have fallen to just £28 a gramme, increasing the prospect of more youngsters becoming hooked.

The illegal narcotics trade accounts for up to 40% of the Afghan gross national product, and is often the only viable source of income in drought-stricken rural communities. The Taliban does not grow it: the insurgents leave that to ordinary people scrabbling to make a living. The only real winners, say the UN, are about 30 powerfully connected drug lords in Afghanistan, Pakistan, Turkey, Albania and Kosovo.

The entire precarious Nato mission in the country is underpinned by the need to divest Afghanistan from its role as the world's leading narco-state. The Kabul government's answer, backed by US policy, is to defoliate poppy fields and prosecute the occasional low-level trafficker. Doing so, however, merely pushes communities deprived of their livelihoods into the arms of the Taliban.

But there is an alternative that would satisfy both the needs of the farmers and help undermine the powerful cartels that control the business. The world is suffering from a shortage of medical diamorphine, the opium-based painkiller marketed as codeine and morphine. The 6100 tonnes of raw Afghan opium harvested in the last year would produce 600 tonnes of medicine. All that is needed is the political will and the finance to make it happen by licensing the poppy-growers and diverting their efforts into legitimate pharmacology rather than into the veins of Europe's addicts.

British government figures show that waging war in southern Afghanistan cost taxpayers £1.48m every single day in 2006. All that has been achieved is a bloodletting on both sides and the expenditure of ever-scarcer Ministry of Defence treasure. If the UK and US governments can invade Iraq against almost universal international diplomatic opposition, they can surely overcome the far more localised objections to undercutting Afghan drug-barons, however well-connected they might be.

Kabul's dilemma is that many of the main players who hold the balance of internal power are heavily involved in trafficking. It feeds and equips their private armies. The West's solution would be to license and buy the crop for medical purposes, removing the source of finance for insurgents and warlords - and to use its military muscle to enforce the strategy against all-comers. The farmers would no longer need the protection of the Taliban, and the West might even turn a legitimate profit on the global medical market.

  • Is Ian's idea workable? E-mail features@theherald.co.uk (with the subject line Think Tank), or write to the Glasgow address on page two. We'll bring you the best responses later in the week, and a new idea next Monday.