Bentley's neice, Maria Bentley Dingwall: "Ours is the strongest case"

Edward Fitzgerald QC, counsel for Bentley's family, said his trial in 1952 was "grossly unfair". His execution was "nothing short of cruel given his mental age, mental defects and epilepsy".

The jury at the time made a plea for mercy, which was ignored.

'Little choice but to convict'

Mr Fitzgerald said the trial judge had acted with "blatant prejudice" and misdirected the jury in such a way that "this conviction simply cannot stand".

He said the trial judge, Lord Chief Justice Goddard, "poured scorn on the defence and the defendant, extolled the virtues of the police officers and left the jury with little choice but to do what he presented to them as their duty, and convict".

The case has always turned on the famous phrase he allegedly uttered shortly before his accomplice shot dead a policeman: "Let him have it."

Craig shortly after his arrest

The Crown alleged at Bentley's trial in 1952 that the crucial words were those of an angry young man urging his accomplice, Christopher Craig to shoot.

Mr Fitzgerald told the court that there was the "gravest doubt" as to whether those words were ever spoken and there was "good reason to doubt the veracity" of the officers involved in the case.

Bentley and Craig always denied that he had said those words.

The same words were used to convict another man, Appleby, in the shooting of a policeman 10 years earlier.

"It is too striking a coincidence that Bentley, a 19-year-old of very limited intelligence, should use precisely the same words," Mr Fitzgerald said.

The BBC's Jane Peel: "New evidence suggests Bentley had a mental age of about 10"

Derek Bentley was mentally handicapped - a fact that never emerged at the trial.

"Had this evidence been available at trial," Mr Fitzgerald said, "it would have cast doubt on some of the assumptions invited".

Far from being homicidal, Mr Fitzgerald said Derek Bentley had shown "complete co-operation" with the police from the time of his capture.

He had not tried to escape and had warned the officers that Craig was dangerous.

Craig ready to testify

Mr Fitzgerald said that Christopher Craig, now 61 and a retired farmer is prepared to give his account of what happened and invited the Court of Appeal judges to call him.

Craig, shot the policeman when he was 16, but was too young to hang and served 10 years in prison.

Bentley's sister Iris mounted a lifelong campaign to quash Bentley's conviction after he was executed at Wandsworth Prison in January 1953.

In 1993 a limited posthumous pardon was granted, accepting Bentley should not have been hanged, although maintaining his guilt.

In November last year the Criminal Cases Review Commission announced the case would be sent back for The Court of Appeal to reconsider.

The campaign to win a full pardon is now being led by her daughter Maria Bentley-Dingwall, who was present in the packed court on Monday.

The appeal continues.