A convicted IRA murderer is to be allowed to give evidence against alleged dissident republican terrorist leader Michael McKevitt at the Omagh bomb civil action, a judge has ruled.

Sean O’Callaghan will be called to try to prove claims that he and McKevitt attended a meeting with other senior Provisionals in the mid-1980s to discuss buying deer hunting rifles to kill soldiers and policemen. O’Callaghan, an informer who says he was once in charge of the IRA’s southern command, has made a series of claims in a statement to the High Court.

Lawyers for victims’ relatives who are suing McKevitt and four other men over the Real IRA attack on Omagh in August 1998, which claimed 29 lives including the mother of unborn twins, wanted permission for O’Callaghan to be allowed to testify at the trial in Belfast. Ruling on his admissibility, Mr Justice Morgan said there was no evidential value to his “assumptions” about McKevitt’s rise in the IRA after Thomas “Slab” Murphy was allegedly appointed Chief of Staff.

But the judge added: “The remainder of the evidence in my view, if true, might assist the plaintiffs in seeking to prove that Mr McKevitt was a relatively senior member of the Provisional IRA during the mid-1980s.

“That fact, if proved, together with the other facts might contribute to a case that Mr McKevitt held such a senior position until the late 1990s. This may have a bearing on the issue of whether the third named defendant (McKevitt) held a leadership position in the Real IRA at the time of the Omagh bomb, as alleged.

“I consider that the relevance test is passed except for the material by way of supposition about what might have happened when Mr Murphy became Chief of Staff.”

As regarding the circumstances surrounding the alleged rifle procurement meeting, O’Callaghan can give direct evidence on claims that he instructed his security officer to tell McKevitt to stop taking vehicles from a Provisional IRA car pool without permission.

The court was told that a further issue he can address centres on his allegations that the IRA’s Chief of Staff in 1985, Kevin McKenna, told him he wanted McKevitt voted onto the paramilitary organisation’s executive.

Mr Justice Morgan said: “In relation to each of these matters he can be subject to cross-examination. He alleges that he appointed his security officer and that Kevin McKenna was introduced as Chief of Staff by him at a meeting.”

O’Callaghan, a special branch agent originally from Tralee, Co Kerry, is now believed to be living in London and will travel to give evidence at a later date.

He was sentenced to two life terms and 529 years imprisonment for terrorist offences, but later released from jail under a Royal Prerogative.

Lawyers for McKevitt, who — along with Liam Campbell, Seamus McKenna, Colm Murphy and Seamus Daly — denies liability in the civil action, had opposed |the admissibility of O’Callaghan’s evidence.