By Sean Rayment, Defence Correspondent

Sgt Danny Nightingale, a special forces sniper who served in Iraq and Afghanistan, was sentenced to 18 months in military detention by a court martial last week.

His sentence was described last night as the “betrayal of a war hero”, made worse because it was handed down in the run-up to Remembrance Sunday.

Sgt Nightingale had planned to fight the charge of illegally possessing the 9mm Glock.

But his lawyer said he pleaded guilty after being warned that he could otherwise face a five-year sentence.

The soldier had hoped for leniency given the circumstances. At the court martial, even the prosecution described him as a serviceman of exemplary character, who had served his country for 17 years, 11 in the special forces.

The court was told that he returned to Britain in a hurry after two friends were killed in Iraq, leaving his equipment — including the pistol — to be packed up by colleagues.

It accepted evidence from expert witnesses that he suffered severe memory loss due to a brain injury.

Judge Advocate Alistair McGrigor, presiding over the court martial, could have spared the soldier prison by passing a suspended sentence. Instead he handed down the custodial term.

Sgt Nightingale and his family chose to waive the anonymity usually given to members of the special forces.

His wife, Sally, said her husband’s sentence was a “disgrace”. She called him a “hero who had been betrayed”. She said she and the couple’s two daughters, aged two and five, faced losing their home after his Army pay was stopped.

The soldier’s former commanding officer and politicians have called for the sentence to be overturned.

Lt Col Richard Williams, who won a Military Cross in Afghanistan in 2001 and was Sgt Nightingale’s commanding officer in Iraq, said the sentence “clearly needed to be overturned immediately”.

He said: “His military career has been ruined and his wife and children face being evicted from their home — this is a total betrayal of a man who dedicated his life to the service of his country.”

Patrick Mercer, the Conservative MP for Newark and a former infantry officer, said he planned to take up the case with the Defence Secretary. Simon McKay, Sgt Nightingale’s lawyer, said: “On Remembrance Sunday, when the nation remembers its war heroes, my client — one of their number — is in a prison cell.

“I consider the sentence to be excessive and the basis of the guilty plea unsafe. It is a gross miscarriage of justice and grounds of appeal are already being prepared.”

In 2007, Sgt Nightingale was serving in Iraq as a member of Task Force Black, a covert counter-terrorist unit that conducted operations under orders to capture and kill members of al-Qaeda.

He also helped train members of a secret counter-terrorist force called the Apostles. At the end of the training he was presented with the Glock, which he planned to donate to his regiment as a war trophy.

But in November 2007, two of Sgt Nightingale’s closest friends, Sgt John

Battersby and Cpl Lee Fitzsimmons, were killed in a helicopter crash. He accompanied both bodies back to Britain and helped arrange the funerals.

In Iraq, his equipment was packed by colleagues, one of whom placed the pistol inside a container that was sent first to the SAS regimental headquarters in Hereford, then to his home where it remained unopened until 2010.

In 2009, Sgt Nightingale, now a member of the SAS selection staff, took part in a 200-mile fund-raising trek in Brazil. He collapsed after 30 miles and fell into a coma for three days.

He recovered but his memory was severely damaged, according to two expert witnesses, including Prof Michael Kopleman of King’s College, London, an authority on memory loss.

In May, 2010, Sgt Nightingale was living in a house with another soldier close to the regiment’s headquarters when he was posted to Afghanistan at short notice.

During the tour, his housemate’s estranged wife claimed her husband had assaulted her and kept a stash of ammunition in the house. West Mercia Police raided the house and found the Glock, still in its container.

Sgt Nightingale’s court martial did not dispute that the pistol had been a gift. It accepted statements from expert witnesses, including Dr Susan Young, a forensic psychologist also from King’s College, London. She said that he probably had no recollection that he had the gun.

The court also accepted that Sgt Nightingale had suffered severe memory loss. But the judge did not believe that he had no recollection of being in possession of the weapon.