They show that prison authorities treated Casement's corpse with contempt, throwing it naked into an open grave and covering it with quicklime. It was a far more degrading treatment than normally meted out to executed prisoners, and more than 50 years later British civil servants still feared the effects on Irish public and political opinion if it was revealed.

The papers, written in 1969 as the security situation in Northern Ireland spiralled into violence, show Home Office and Northern Ireland Office bureaucrats agonising about how much they should reveal of the degrading treatment shown to a hero of the nationalist community.

For Casement's bones had been at the centre of a tussle between Britain and the new state of Ireland for almost 50 years.

While the other heroes of the Easter Rising, such as Pádraig Pearse and James Connolly, were executed in Dublin after military tribunals and buried there, Casement was treated as a common traitor and buried in an unmarked grave inside Pentonville prison, north London, after his execution on August 3 1916.

From 1924 onwards, Irish governments supported the Casement family's petition for his body to be returned home for burial in County Antrim. It was only in 1965, after an appeal by Seán Lemass, another veteran of the rising and by then Taoiseach, that the grave was opened and bones removed from beneath the skeletons of two hanged murderers. An Irish government official witnessed this.

Soon after the state funeral given to Casement by the Irish government, with his coffin passing 1 million mourners, doubts were voiced about the authenticity of the remains handed over by Britain.

Irish newspapers alleged Casement's body must have been treated the same way as those of Pádraig Pearse, James Connolly and other executed republicans, and "rendered" to nothingness by quicklime. They accused the British of substituting the bones of another criminal.

One newspaper claimed the skeleton afforded such honours in the Irish national cemetery of Glasnevin was really that of Dr Crippen, the murderer hanged in Pentonville in 1910.

The British government refused to comment on the allegations, but the authorities in Dublin played down the idea, reminding critics that one of their own number had witnessed Casement's removal.

Embarrassment



The row simmered on and it became part of republican lore that Casement's coffin contained only stones put in to lessen embarrassment to Lemass.

Then, in October 1969, a letter from Sir Knox Cunningham, the Ulster Unionist MP for South Antrim, stung Whitehall into action. He wrote to Jim Callaghan, then home secretary, saying a constituent had asked him to find out if it was true that Casement, a South Antrim man, had been rendered.

The security situation in Northern Ireland was very tense in 1969 and earlier that month the first RUC officer to die in the Troubles had been gunned down by loyalist terrorists. But the killing had stunned the province and the British government was hopeful of nipping the violence in the bud.

Sensing a conspiracy behind the Casement inquiry, Home Office officials sought help from other departments because they had found original records of the burial and knew that, although his bones did survive, there had been every intention to destroy any trace of him.

SW Bennett, a Prison Commission official, wrote: "In 1924 it was stated [in prison records] that the body was buried without clothing and without a coffin in quicklime."

AS Pratley, of the Northern Ireland Office, wrote: "It is difficult to judge how much embarrassment, if any, might be caused by a straight confirmation that Casement was buried without a coffin in quicklime. The most probable consequence would be a reopening of the argument about the authenticity of the remains sent to Ireland in 1965. It is also possible, however, that a sense of outrage would be aroused in Eire by an official confirmation that instructions were given to bury Casement without a coffin. We cannot claim this was standard practice."

Papers from the National Archives, show that, probably because of his homosexuality and his treachery, Casement was subjected to the ultimate indignity in death. ER Colwyn, another Home Office bureaucrat, said: "The position appears to be that it was practice always to use quicklime, but that the use of coffins was left to the discretion of the prison. The instructions for Casement's burial were quite specific - a coffin was not to be used."

According to the papers, the quicklime had not had the expected effect of dissolving Casement's bones because, in certain conditions of soil and temperature, the treatment actually preserved human remains - so the bones sent to Ireland were indeed those of the nationalist icon.

But the bureaucrats were still worried about being too open. "It would seem advisable," Mr Pratley wrote, "to avoid specific reference to the absence of a coffin."

Eventually it was decided a limited honesty would be the best policy and a letter was drafted for Shirley, now Baroness, Williams, then minister of state, to send to Sir Knox Cunningham saying Casement was buried in quicklime which "was the practice that obtained at the time".

But despite the mandarins' fears, the information was never made public and the idea that the Casement coffin was full of stones was repeated as late as 1998 in Sinn Féin's newspaper An Phoblacht, although immediately contradicted by the historian Proinsias Mac Aonghusa, who unwittingly denied that quicklime had been used on the great Irish martyr.