It was just the sort of good news the British military in Helmand needed. Soldiers engaged in Operation Panther’s Claw, the huge assault against insurgent strongholds last week, had discovered a record-breaking haul of more than 1.3 tonnes of poppy seeds, destined to become part of the opium crop that generates $400 million a year for the Taliban.

Ministry of Defence officials more used to dealing with negative stories about the British operation in southern Afghanistan swung into action to extract the maximum benefit from this unexpected PR coup.

A press release hailed the success of the offensive, and armoured vehicles were hastily laid on to allow the media, including the Guardian, to visit the site where the seizure was made, an abandoned market and petrol station that was still coming under sustained enemy fire when the reporters arrived.

Major Rupert Whitelegge, the commander of the company in charge of the area, tugged at one of the enormously heavy white sacks.

“They are definitely poppy seeds,” he said emphatically.

Except they weren’t. Analysis of a sample carried out by the UN’s Food and Agriculture Organisation in Kabul for the Guardian has revealed that the soldiers had captured nothing more than a giant pile of mung beans, a staple pulse eaten in curries across Afghanistan.

Embarrassed British officials have now admitted that their triumph has turned sour and have promised to return the legal crop to its rightful owner.

Don’t the Brits allow farmers into their army anymore? Or vegetarians?