Journalist Toby Harnden, who wrote a book in which he alleged that an Irish police officer had colluded with the IRA, has declined to give evidence about his claim.
He was due to appear tomorrow at a judicial inquiry in Dublin, the Smithwick Tribunal, which is looking into the killing of two RUC men, Chief Superintendent Harry Breen and Superintendent Robert Buchanan, near the Irish border in 1989.
Harnden wrote about the killings in his 1999 book, Bandit Country - The IRA and South Armagh.
He gave no reason for refusing to appear, saying only that it followed discussions with his new employers, Associated Newspapers.
Harnden became the Daily Mail's US editor at the beginning of the year, having previously worked for the Daily Telegraph for 17 years. He was the Telegraph's Ireland correspondent from 1996 until 1999.
Jim O'Callaghan, the barrister acting for a policeman alleged to have colluded with the IRA, described the development as "a matter of extreme concern".
He said the reason the tribunal had been established was because of the allegations contained in Harnden's book. He had been anxious to cross-examine the journalist.
The tribunal's chairman, Judge Peter Smithwick, said he hoped Harnden would be able to give evidence at a later date and that the tribunal would talk to the solicitors at Associated Newspapers to facilitate the Harnden's attendance.
Sources: Irish Times/BBC