A Royal Marine who is in prison for the fatal shooting of a Taliban fighter in Afghanistan should now be freed, leading judges have heard.

The plea for the release of Sergeant Alexander Blackman was made by his QC at the start of a sentencing hearing in London today.

A panel of five judges at the Court Martial Appeal Court are due to sentence Blackman for diminished responsibility manslaughter following the recent decision by the court to overturn his murder conviction for the 2011 killing.

The decision will now be announced on Tuesday.

Blackman, 42, from Taunton in Somerset, watched today's proceedings via video link from prison.

His wife Claire and a large number of supporters - who had earlier waved banners outside the Royal Courts of Justice appealing for Blackman to be freed - sat in the packed public gallery.

MP for South Dorset Richard Drax has been supporting the Blackman family with the appeal.  

When the court overturned the murder conviction, the former Coldstream Guard told the Daily Echo he was "absolutely delighted" about the decision.

At today's proceedings, Jonathan Goldberg, making submissions in mitigation, told Lord Chief Justice Lord Thomas and the other judges that "at the forefront of our submission is the plea that he should be released today".

He said that "the incarceration of almost three and a half years which he has already served is already too much for his crime".

The judges had previously ruled that Blackman was suffering from an "abnormality of mental functioning" at the time of the incident.

When the court overturned the murder conviction, the judges found that the incident was not a "cold-blooded execution" as a court martial had earlier concluded, but the result of a mental illness - an "adjustment disorder".

Blackman was convicted of murder in November 2013 by a court martial in Bulford, Wiltshire, and sentenced to life with a minimum term of 10 years.

That term was later reduced to eight years on appeal because of the combat stress disorder he was suffering from at the time of the killing in Helmand province while serving with Plymouth-based 42 Commando.

The judges said that Blackman had been "an exemplary soldier before his deployment to Afghanistan in March 2011", but had "suffered from quite exceptional stressors" during that deployment.

They found that his ability to "form a rational judgment" was "substantially impaired".

Blackman shot the insurgent, 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.

He 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.''

The shooting was captured on a camera mounted on the helmet of another Royal Marine.

During his trial, Blackman, who denied murder and was known at that stage as Marine A, said he believed the victim was already dead and he was taking out his anger on a corpse.