UN figures released today show that poppy cultivation in the Afghan province of Helmand, where most British troops are deployed, fell by a third this year.
This is the first major breakthrough for Britain's costly campaign against networks of drug-dealers in the area, which has lasted for several years.
A 33 per cent drop in the area of land (down to 69,833 hectares) devoted to opium poppy growing was attributed in large part to farmers switching crops in order to cash in on high wheat prices.
The annual UN Afghanistan opium survey attributed this success in Helmand to the strong leadership of Gulab Mangal, the province's governor, who helped to establish corn-growing areas around the city of Lashkar Gah.
However, the report by the UN Office on Drugs and Crime (UNODC) showed that despite this fall, there were till more poppies being grown than when British troops were deployed to Helmand in 2006.
It was also noted that opium output has not fallen in line with cultivation, as poppy farmers become more skilful at producing the world's heroin supply, and can squeeze more opium resin from poppy bulbs.
This trend was evident across Afghanistan. While the overall area of land used for poppy cultivation fell by 22 per cent, production only shrunk by 10 per cent. Afghanistan's drug industry now produces 56kg of opium per hectare, a 15 per cent rise on last year.
Antonio Maria Costa, head of the UNODC said: "At a time of pessimism about the situation in Afghanistan these results are a welcome piece of good news and demonstrate that progress is possible."
Officials in Kabul said that the improvement was largely due to market forces - last year's surge in the price of corn, combined with the on-going collapse in the value of opium due to overproduction.
Afghanistan now produces 90 per cent of the world's heroin. The report concluded that "the bottom is starting to fall out of the Afghan opium market".
