British lawyers have joined the call on the Canadian Government to intervene over Omar Khadr, the youngest detainee at Guantanamo Bay who has now spent a quarter of his life in captivity there.

The Criminal Bar Association is urging action by the Canadian Prime Minister to seek the repatriation of Mr Khadr, who is now 20 but who has been detained at Guantanamo Bay since he was 15.

Mr Khadr, a Canadian, is the only person in modern history to be tried for war crimes that he allegedly committed as a minor.

He has twice been brought before military commissions in Guantanamo and twice had charges against him dismissed. Mr Khadr was then returned to detention without charge.

Andrew Hall, QC, the former chairman of the Criminal Bar Association, says that all other allies of the United States, have acted to protect their detained citizens and succeeded in having them repatriated.

“The Canadian Government should follow the precedent of other US allies and assert its sovereign interest by providing diplomatic protection to its citizens,” he said.

Mr Khadr is alleged to have committed five violations of the Military Commissions Act: murdering a US soldier during combat; attempting to murder US or coalition forces; conspiracy; supporting terrorism; and spying.

He has been detained in Guantanamo Bay for five years, much of it in a maximum security prison, in a cell with no windows, awaiting a military trial.

His lawyers say that due to his age when he was taken prisoner, he should have been considered a child soldier and shouldn't be there at all.

But Mr Khadr faces serious charges and, if convicted, could face up to life in prison.

He was captured in eastern Afghanistan, a region notorious for harbouring members of al-Qaeda and the Taliban. In July 2002, US special forces were patrolling the area when they got a tip that some al Qaeda members were holed up nearby.

A unit led by Sergeant Layne Morris approached a walled compound. Al-Qaeda gunmen opened fire, killing Morris's interpreters instantly. After several hours of fighting, the compound was completely destroyed. When the soldiers entered, someone threw a hand grenade at them. One of the medics, Sergeant Christopher Speer, was killed. Mr Khadr was found afterwards, barely alive, lying in the rubble and blinded in one eye.

Explore Law

• Columnists

• Law Panel

• Law Reports

• Student Law

Times Recommends

• The best legal yarns this Christmas
• Legal school 'earned £1m by exploiting bar course'
• Axe may fall on 5,000 more City lawyers