A British special forces sniper was on Wednesday convicted of unlawfully possessing a pistol and more than 300 rounds of ammunition, in a case which shone a rare spotlight on the army's elite SAS unit.

It was a second court martial conviction for Danny Nightingale, a 38-year-old veteran of the conflicts in Afghanistan, Bosnia and Northern Ireland, after the first was quashed by the Court of Appeal.

His original conviction sparked an outcry in Britain, with supporters declaring it a betrayal of a war hero who dedicated 17 years to the military. More than 100,000 people signed a petition for his release.

But after a second trial in Wiltshire, southwest England, the father-of-two was on Wednesday found guilty of two charges of possessing a Glock 9mm and 338 rounds. Gun ownership is severely restricted in Britain and possessing handguns is illegal.

He was released on bail and sentencing was adjourned.

The pistol was found in Nightingale's house in September 2011 while he was serving in Afghanistan, but he said he had no knowledge of the weapon and someone else had put it there.

In his first trial, he claimed the pistol was a trophy brought back from the war in Iraq, and he had accumulated the ammunition from training sessions in Britain.

He blamed the change in his story on an illness suffered while he was taking part in an endurance event in Brazil four years ago. He has now been medically discharged from the army.

During the trial, several members of the SAS gave evidence anonymously, including Nightingale's former flatmate, referred to in court only as Soldier N.

Soldier N has himself been convicted for possessing a Glock 9mm pistol that he brought back from Iraq, and he told Nightingale's trial that his behaviour was not unusual.

"You go on operations, you want to bring back a trophy, as our grandfathers did in the war," he said.