Lance Corporal in the Coldstream Guards hit trigger switch of suicide bomber whose device then exploded,
The 20-year-old marksman, a Lance Corporal in the Coldstream Guards, hit his target from 930 yards (850 metres) away, killing the suicide bomber and five others around him caught in the blast.
The incident in Kakaran in southern Afghanistan happened in December but has only now been disclosed as Britain moves towards the withdrawal of all combat soldiers by the end of the year.
Lt Col Richard Slack, commanding officer of 9/12 Royal Lancers, said the unnamed sharpshooter prevented a major attack by the Taliban, as a second suicide vest packed with 20kg (44lbs) of explosives was found nearby.
The same sniper, with his first shot on the tour of duty, killed a Taliban machine-gunner from 1,465 yards (1,340m).
Several hundred British and Afghan soldiers were carrying out an operation in December when they were engaged in a gun battle with 15 to 20 insurgents.
“The guy was wearing a vest. He was identified by the sniper moving down a tree line and coming up over a ditch,” said Lt Col Slack. “He had a shawl on. It rose up and the sniper saw he had a machine gun.
“They were in contact and he was moving to a firing position. The sniper engaged him and the guy exploded. There was a pause on the radio and the sniper said, ‘I think I’ve just shot a suicide bomber’. The rest of them were killed in the blast.”
It is understood the L/Cpl was using an L115A3 gun, the Army’s most powerful sniper weapon.
The armed forces are gradually decreasing their presence in Helmand province, handing over security of the country to the Afghan armed forces.
Last month, three major bases were closed or handed over to Afghan control. At the height of the campaign, there were 137 bases across Helmand province — now there is only one base outside Camp Bastion, Sterga 2, which is staffed by a company from 4 Scots and the 9/12 Royal Lancers.
The sniper incident is one of a dwindling number of gun battles between British forces and the insurgents. In total, 448 UK soldiers have died since 2001, but far fewer have been injured in the most recent tour, with Afghan forces now leading 97 per cent of the security operations across the country.
On Monday, at Sterga 2 — the last British front line base in Afghanistan — soldiers said they were looking forward to returning home and hoped their work would help the Afghans achieve stability.
Sterga 2 stands on a plateau above the Helmand river, about 18 miles south-east of Camp Bastion. Between Bastion and Sterga 2 is the “protected zone”, next to the river, where the local population is living under the protection of the Afghan armed forces.
The camp has only come under attack once, and that was when it was being built last August. “In my tour in 2007, I had seven guys injured while they were actually inside the base,” said Lt Col Slack. “We had rocket attacks every day. This base hasn’t been attacked since it was built. It feels like it is time to go.”
Capt Ed Challis, who is in charge of Sterga 2, said he was hopeful about the future of Afghanistan.