Challenge to Real IRA conviction

McKevitt, 54, was sentenced to 20 years in 2003 for directing terrorism and membership of an illegal organisation.

His lawyers were granted permission to go the Irish Republic's Supreme Court.

They claim the defence team in his trial was not given full information about the tax affairs of chief witness David Rupert, an FBI and British agent.

In December 2005, an attempt by McKevitt to have his conviction overturned failed at the Court of Criminal Appeal.

His lawyers had sought to have his conviction quashed by challenging the credibility of Mr Rupert, a secret agent of the FBI and the British security service.

McKevitt, from Blackrock, County Louth, was the first person to be convicted in the Republic for the offence of directing terrorism, which was introduced after the 1998 Real IRA bomb attack in Omagh.

The explosion claimed the lives of 29 people, including a woman pregnant with twins.

He also received a six years concurrent prison sentence for membership of an illegal organisation which the court said was the Real IRA.

Mr Rupert was reported to have infiltrated the Real IRA and attended Real IRA Army Council meetings where McKevitt was present.