Opium production in Afghanistan has again hit record levels and is likely to boost terrorism and increase supply of cut price heroin around the world, the United Nations has warned.

Three years after British combat troops and aid officials left the country’s Helmand province, farmers there are now estimated to have a third of arable land set aside for drug production.

More than 90 per cent of the heroin on Britain’s streets is thought to come from the country and the UK spent tens of millions of pounds trying to tackle the trade and wean farmers off the crop.

But figures released from the UN’s drugs and crime agency said production had almost doubled in the past 12 months. Helmand, the hub of opium production, has seen the the area under poppy rise by four-fifths.

The UN said the increase: “Will probably further fuel instability, insurgency and increase funding to terrorist groups in Afghanistan.