Tuesday is market day at Camp Bastion, when dozens of nomads who have settled close to the base are allowed in to sell souvenirs and treats to the troops. Backs of vans are stacked high with pashminas, scorpions are embedded in ashtrays and a fervent trade in budget price counterfeit DVDs goes on.

At the top end of the scale are the precious stones mined in northern Afghanistan. Rubies sell for $60 apiece, emeralds for double that. Soldiers bargain for a special gift for the wife back home, the dealers armed with tiny torches and magnifying glasses to prove the prestige of the jewel.

But with yesterday's bazaar came the unexpected, when a security alert was triggered by a suspect vehicle.

The traders are the only "outsiders" allowed in the camp, and searches are understandably tight. But a potential threat was detected and a wide area of the camp cordoned off for several hours as investigations were carried out.

The dusty avenues of Camp Bastion cleared as tannoys over the settlement warned residents to stay away from the area. Taking to hard cover was advised, but in a sea of tents it would have been difficult. Dinner time was cancelled at the main base canteen.

For many it was a high price to pay for a trinket but, even among the most trivial of pleasures, such as shopping for cheap movies and cartons of cigarettes, the potential threat to safety is ever present.

Yesterday also brought further British casualties at Camp Bastion, with three soldiers injured by a roadside bomb. Their injuries are not thought to be critical.

Meanwhile, the head of the armed forces in Britain visited an army outpost in Afghanistan this week and admitted the challenge remained "huge and daunting" but that progress was being made.

Sir Jock Stirrup, chief of defence staff, visited a base just outside Garmsir and said that the small town was no longer the "full scale battlefield" it was a few weeks ago.

"The scale of the total challenge remains huge and daunting, but each time I've come here I see we've moved further. The last time I was down in this part of the world, I wasn't able to come into the area of the town - it was a full-scale battlefield."