Judgment has been reserved in the appeal by Nicholas Mullen, the last republican prisoner being held in a British jail.
Mullen (50), who was jailed for 30 years in June 1990 for conspiracy to cause explosions at the IRA's "bomb factory" in Clapham, south-west London, had fled to Zimbabwe with his girlfriend and young daughter, but was arrested on his return.
His counsel, Mr Colin Mackay QC, told the Court of Appeal in London that Mullen's conviction was unsafe and should be quashed because the way he was brought back to England violated both international and Zimbabwean law.