A 14-year-old boy was promised $80 (£50) by the Taliban to set off a device that killed a British marine in Afghanistan, an inquest has heard.

Stephen Curley, 26, was killed instantly when a roadside bomb was detonated in Helmand. A few days after Curley was killed, the boy was handed in by his father and confessed to setting off the IED, the inquest in Exeter was told.

The boy, named as Aga Wali, confessed to the Afghan police after the Taliban went back on its deal to pay him and told him he ought to have carried out the attack to help his country.

He was not handed over to British security or intelligence officers but was questioned by the local Afghan chief of police.

It is believed the boy was sentenced to jail but it is not known how long he will serve or if he is still in custody.

Curley's widow, Kirianne, 28, only learned of the teenager's apparent involvement shortly before the hearing.

Lieutenant Colonel Paul James, who was in charge of operations with 40 Commando Royal Marines at the time, said: "I received a report from the Afghan national police that a 14-year-old boy had been handed in by his father for being the trigger man in an IED attack."

James said the date corresponded to the day Curley was caught in the explosion in May last year. He added: "The father was concerned that his son was embarking upon a life as a fighter with the Taliban and feared for his life.

"He said Aga Wali had been told he would be paid 80 US dollars but when he went for payment they said aggressively he should be fighting for ideological reasons and not financial gain.

"Aga Wali left angrily and felt betrayed. The boy was detained briefly within the national directorate of security before being processed through the courts and a sentence of imprisonment was imposed of an uncertain period of time." Another witness, Captain Dom Rogers said he was present when the boy was questioned. "In my presence he admitted activating an IED and acting as the trigger man. He was unable to read a map but was able to describe the ground and it fitted with that where Corporal Curley was wounded fatally," he said.

The fatal patrol was organised as part of an effort to reassure local people concerned about their safety. Curley's wife had given birth to their son, William, 18 weeks before he was killed. At the time of his death she said: "It is impossible for me to express what my husband meant to me. Daddy to our 18-week-old son William and my partner in crime, Stevie was my purpose, what makes me tick.

"A man of few but powerful words when it mattered, he lived by the motto 'If you're not living life on the edge, you're taking up too much room.'"