A Royal Marine found guilty of murdering an injured Afghan fighter has lost a bid to take his battle to overturn his conviction to the UK's highest court.

Three leading judges refused to give Sergeant Alexander Blackman permission to appeal to the Supreme Court.

Earlier this year, Blackman's appeal against conviction was rejected by Lord Chief Justice Lord Thomas, Sir Brian Leveson and Lady Justice Hallett at the Court Martial Appeal Court in London.

Today, Lady Justice Hallett, sitting at the same court, announced their decision to refuse his application to continue his fight at the Supreme Court.

After being convicted last November at a court martial in Bulford, Wiltshire, Blackman was sentenced to life with a minimum term of 10 years.

He was also ''dismissed with disgrace'' from the Royal Marines after he had served with distinction for 15 years, including tours of Iraq, Afghanistan and Northern Ireland.

Although his conviction appeal was dismissed in May, the three judges allowed his sentence challenge, reducing the 10-year minimum to eight years - the least he must serve before he can be considered for parole.

The reduction was made because of the combat stress disorder he was suffering at the time of the incident.

Appeal judges said the particular stresses affecting Blackman should have been ''accorded greater weight as a mitigating factor'' when he was sentenced by the court martial.

Lord Thomas said at the time: "On all the evidence before us, it is clear that in the events surrounding the murder of the insurgent, the appellant acted entirely out of character and was suffering from combat stress disorder.''

The killing happened in Helmand province in 2011 while Blackman, who is known as Al, was serving with Plymouth-based 42 Commando.

He shot the Afghan, who had been seriously injured in an attack by an Apache helicopter, in the chest at close range with a 9mm pistol before quoting a phrase from Shakespeare as the man convulsed and died in front of him.

Blackman told him: ''There you are. Shuffle off this mortal coil, you c***. It's nothing you wouldn't do to us.''

He then turned to comrades and said: ''Obviously this doesn't go anywhere, fellas. I just broke the Geneva Convention.''

Blackman, who denied murder, said he believed the victim was already dead and he was taking out his anger on a corpse.

He has said he felt ashamed at his action, describing it as a ''stupid lack of self-control and lapse in judgment''.