A teenage soldier killed alongside five colleagues in a bomb blast in Afghanistan had volunteered to take the place of a fellow private at the last minute, an inquest heard.

Private Christopher Kershaw, of Bradford, had offered to stand in as the driver of a Warrior armoured vehicle which was blown up just minutes later during a patrol in March last year.

The 19-year-old died alongside Sergeant Nigel Coupe, 33, Corporal Jake Hartley, 20, and Privates Anthony Frampton, 20, Daniel Wade, 20, and Daniel Wilford, 21, during the incident in Helmand Province on March 6, 2012.

An inquest into their deaths at Oxford Coroner’s Court yesterday heard that it was most likely that Sgt Coupe, a member of 1st Battalion The Duke of Lancaster’s Regiment, and his comrades, all members of The Yorkshire Regiment’s 3rd Battalion, were either killed or knocked unconscious by the huge blast, and unaware of what happened afterwards.

The Warrior, known by the callsign K12, was patrolling with another vehicle when it was hit by an improvised explosive device about 25 miles north of the capital of Helmand, Lashkar Gah.

The force of the explosion turned the it upside down and blew off its gun turret. Ammunition on board the vehicle ignited, causing a fierce fire.

The attack, the deadliest single enemy attack on UK forces in Afghanistan since 2001, was claimed by the Taliban.

The inquest heard that the patrol was meant to leave earlier that day but was delayed because of a sandstorm. It eventually left shortly after 6.30pm, and was blown up minutes later.

Fellow soldiers in a second Warrior vehicle, given the callsign K13, reported hearing an explosion then seeing a “fireball” as it ignited.

The inquest was attended by relatives of the dead soldiers, including Pte Kershaw’s mother Monica – who carried a photo of her son – and his father Brian and his wife Sharon. In a statement read to the court, Private Luke Stones, of 3 YORKS, described how Pte Kershaw – who was driving the Warrior – had volunteered to take the place of another soldier on the patrol. “Private Butler would have been the driver of K12 but he was returning from the shower and as a result Pte Kershaw offered to take his place,” he said.

Pte Stones, who was the gunner in the second Warrior, said he heard a “large explosion” only five minutes after leaving the base.

“Around 20m to my front was a large fireball which had flames reaching around it,” he said.

“I stood staring at the fireball not really understanding what I was looking at.”

The blast had blown the armoured vehicle on to its side, and blew its gun turret off, the inquest heard.

Reports from two pathologists said it was most likely that all six were either killed or rendered unconscious by the blast, leaving them unaware of what happened afterwards.

As they cleared a safe path to the Warrior and tried to put the blaze out, colleagues from the second vehicle described hearing ammunition ignite and ricochet inside the stricken vehicle.

A statement from Pte Aiden Walker said: “I believe that no-one in the Warrior was alive and could have survived the explosion.”

Pte Kershaw, of Idle; father-of-two Sgt Coupe, of Lytham St Annes, Lancashire; Pte Wade, of Warrington, Cheshire, who was about to become a father; Cpl Hartley, of Dewsbury, and Pte Frampton and Pte Wilford, both of Huddersfield, had all only been in Afghanistan for a few weeks.

The tragedy was, and remains, the biggest single loss of life for British forces in Afghanistan since an RAF Nimod crash killed 14 people in September 2006.

The inquest continues.