Derek's brother Dennis Bentley: 'There are no winners in a case like this'

The court also granted a full posthumous pardon to Mr Bentley who was convicted of murdering the policeman in a failed burglary in 1952, although it was his accomplice who fired the gun that killed him.

Mr Bentley's family immediately called for a full investigation into the miscarriage of justice.

Iris Bentley, who led the family's battle, is not alive to savour victory

Niece Maria Bentley-Dingwall said on the steps of the High Court: "We definitely want a public inquiry now."

Her solicitor confirmed that a compensation claim would be lodged, probably on behalf of the estate of Bentley's sister Iris, who died in 1997.

The three Appeal Court judges said Mr Bentley had been denied a fair trial because of the way the original trial judge, Lord Chief Justice Goddard, summed up the case.

The victory was the culmination of a ceaseless campaign begun by Iris Bentley.

Time to celebrate: Maria Bentley-Dingwall

In 1993 she won a limited pardon for her brother when the then Home Secretary, Michael Howard, agreed that he should not have been executed on 28 January 1953.

Ms Bentley-Dingwall, 35, said after the decision: "He was never meant to hang and the one thing that torments me today is that Derek will never be able to walk free and that my mother Iris is unable to be with me."

Mr Bentley, who was aged 19 but had a mental age of 11, played no physical part in the killing of PC Sidney Miles during the Croydon warehouse break-in.

Christopher Craig fired the fatal shot

His 16-year-old accomplice Christopher Craig fired the fatal shot, but police witnesses said Mr Bentley had encouraged him to shoot, shouting: "Let him have it Chris."

Both men denied these words were spoken.

Craig, who was also convicted, was too young to be hanged and Mr Bentley went to the gallows instead.

Craig later made a statement expressing his relief at the Appeal Court decision and his sorrow over the "pain and misery" of his actions.