British troops fighting a bitter insurgent war in Helmand province could be placed in even more danger if the Afghan government approves a new US-backed programme to eliminate the country's poppy-crop by spraying it with herbicide.

UK officials leading the battle against the burgeoning opium output from the poppies say the policy would backfire by wiping out the livelihoods of tens of thousands of local farmers and could drive them into the arms of the Taliban.

It might also wipe out food crops grown alongside the poppies and hand the insurgents a major propaganda victory by allowing them to claim that the West was waging chemical warfare on civilians.

While President Hamid Karzai continues to resist American efforts to begin widespread spraying from the air, sources say he looks likely to approve a new scheme to use hand-sprays to destroy crops in selected areas.

Helmand, where 7000 British soldiers are engaged against Taliban fighters on a daily basis, produced about half of last year's bumper national crop of more than 8000 tonnes of raw opium. That, in turn, is refined down to more than 1000 tonnes of heroin smuggled out through Pakistan Turkey and Iran and sold on the streets of Europe.

At least 260 addicts in Scotland died from heroin overdoses in 2006, and more than 1000 in England and Wales, according to government figures released yesterday.

US pressure on the Afghan government is being masterminded by Ambassador William Wood. He earned the nickname "Chemical Bill" in his previous post in Colombia due to his enthusiasm for spraying illegal coca fields with herbicides.

The US is now advocating the use of glyphosate, a defoliant which it claims is less environmentally toxic than aspirin or caffeine. European diplomats say the toxicity is irrelevant. They fear any widespread use will be seen as a Western assault on the Afghan way of life and could destabilise both the Nato security and reconstruction effort and even the Karzai government.

Both the Pentagon and the CIA have lined up as surprising allies of the Europeans, lobbying against their own State Department's policy on drug eradication and its endorsement by the White House.