The theft of the Irish Crown Jewels from Dublin Castle rocked the British Establishment's seat of power in Ireland. A century later, new research has challenged the findings of a 1908 vice-regal inquiry into the scandal and points the finger of blame at Francis Shackleton, the brother of the polar explorer Ernest.

The theft, four days before King Edward VII was to make a state visit to Ireland, enraged the monarch. The jewels - the star and badge of the Order of St Patrick, made of Brazilian diamonds, emeralds and rubies - were never recovered and the theft become a cause célèbre for nationalists fighting for independence from Britain.

Sean J. Murphy, an historian conducting a review of all the available evidence, believes that Shackleton was the thief but that he skilfully protected himself by using his brother's prestige and threatening to expose a homosexual group at Dublin Castle.

The original inquiry exculpated Shackleton by name - the only individual afforded this privilege - while accusing Sir Arthur Vicars, the Ulster King of Arms, saying that he “did not exercise due vigilance or proper care as the custodian of the regalia”.

Shackleton was the Dublin Herald and shared a house with Vicars, who held the only keys to the safe where the jewels were stored.

“I have seen the records of Shackleton's interviews and they are a masterpiece of control of his interrogators,” Mr Murphy told The Times. “Shackleton is threatening to reveal all sorts of damaging information if he is pressed too hard.” He believes that this was related to rumours of homosexual activities inside the castle, quoting from a letter written by an official that refers to Shackleton and others being “addicted to certain practices”.

Five years later, in 1913, Shackleton was convicted of fraud after cheating a widow out of her savings.

The Gaelic American, an Irish-American newspaper, claimed that wild parties were held by Vicars in the Office of Arms. On one occasion someone relieved him of the keys to the safe, removed the Crown Jewels and returned them to him by post days later. “I think Shackleton witnessed this and realised how easy it was to get the jewels,” Mr Murphy said.

Vicars never got over the affair. His will was released only after languishing under the censor for 55 years. He wrote: “I was made a scapegoat to save other departments responsible ... they shielded the real culprit and thief, Francis R. Shackleton. My whole life and work was ruined by this cruel misfortune and by the wicked and blackguardly acts of the Irish Government.”

He was shot dead in front of his wife in an IRA raid on his home in 1921.

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