For Christie Walsh, there is one aspect of the death of his great-uncle Patrick that sums up his family's 89-year search for justice. "He was shot for not putting on his hat," Mr Walsh said. "How ludicrous and cruel is that?"

For Christie Walsh, there is one aspect of the death of his great-uncle Patrick that sums up his family's 89-year search for justice. "He was shot for not putting on his hat," Mr Walsh said. "How ludicrous and cruel is that?"

At 8am, on 27 December 1915, a firing squad lined up near the Greek port of Salonika and took aim at Private Patrick Downey, 19, from Limerick. One witness said that when Pte Downey heard his death sentence, he laughed and said: "That is a good joke. You let me enlist and them bring me out here and shoot me."

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This weekend, relatives of Pte Downey and 25 other Irish soldiers who were executed while serving in the British Army during the First World War, hope to revive their memory in a final attempt to secure them a pardon with the help of a diplomatic offensive by the Irish government.

The families of the soldiers will present a petition at Downing Street before Remembrance Sunday, which this year marks the 90th anniversary of the start of the war, which claimed nearly a million British Empire lives, including 50,000 Irishmen.

Mr Walsh, 61, a Dublin taxi driver, who will be in the Irish delegation, said: "This could be our last chance. Of course, I never met my great-uncle Patrick but the sense of injustice in our family at his death has never gone away. My mother often spoke of what had happened, how he had been shot for no reason. The tale was that he had been court-martialled for refusing an officer's order to put on his cap. As far as my mother was concerned, he was murdered."

Although the relatives of the 26 Irish soldiers have made such demands before, they are making their initiative for the first time supported by the full diplomatic and political weight of the Irish government.

Officials at the Ministry of Defence are considering a report from Dublin which, in stark language, demands pardons for each soldier because the British Army had ignored "clear evidence" that should have saved each one from the firing squad.

The contents of the confidential report, based on records from British archives and expert opinion sought by the Irish, suggest the Irish soldiers - who were among 306 British and Commonwealth troops executed during the war - were shot on the orders of senior officers who were paranoid about discipline in their units.

Dermot Ahern, the Irish Foreign Affairs Minister, said: "The files make heartbreaking reading. They refer to medical conditions, personal problems, deaths of family members and other extenuating circumstances that are simply not taken into account. In most cases, there are written notes from superior officers that bluntly call for an example to be made. Guilt or innocence was a secondary consideration."

Dublin has also pointed to new evidence of anti-Irish sentiment among British officers that shows a disproportionate number of Irish troops were executed. The Irish represented 8 per cent of those condemned to death, but they made up just 2 per cent of the Army.

The campaigners, led by the pressure group Shot At Dawn, say many of the soldiers were unrepresented at their hearings and not allowed to make defence statements during often shambolic proceedings for charges ranging from cowardice to striking an officer.

For Pte Downey, who lied about his age to join the Leinster Regiment, the only record of his trial is three pages of handwritten notes. They show that while fighting a bitter winter campaign in the Balkans against Bulgarian troops, Pte Downey was arrested for disobeying an officer on three occasions, the last of which was refusing to put on his cap.

Senior officers changed the charge faced by the Irishman, who had a record of minor offences, from a non-capital offence to one that carried the death penalty and, contrary to military law, allowed the defendant to plead guilty.

When General Bryan Mahon, the commanding officer in Greece, wrote to approve the death sentence, he said: "Under ordinary circumstances, I would have hesitated to recommend the capital sentence be put into effect as a guilty plea has erroneously been accepted. But the condition of discipline in the battalion is such as to render an exemplary punishment highly desirable."