The British House of Lords has paved the way for Mr John Gilligan, who faces a charge of murdering the journalist Veronica Guerin, to be returned to Ireland for trial.
Lawyers for Mr Gilligan (47) argued that he had been unlawfully held in custody so that evidence could be gathered against him following "collusion" between Irish and British police and Customs and Excise.
They asked the House of Lords, Britain's highest appeal court, to rule that extradition was unlawful because the offences contained in the Irish warrant did not correspond to English offences. They also contended that they should have been entitled to argue before magistrates or the British High Court that there had been an abuse of process.
But yesterday, following a two-day hearing, Lord Browne Wilkinson and four other law lords unanimously rejected the claims.
Lord Browne Wilkinson said the appeal panel would give its reasons at a later date. It is understood that no moves will be made to return Mr Gilligan to Ireland before that occurs.
Mr Gilligan faces charges in the State of the murder of Ms Guerin, of unlawfully importing cannabis and of the possession of cannabis and firearms.
It took the law lords just under 15 minutes to reject Mr Gilligan's appeal against a High Court refusal to allow his lawyers to pursue abuse-of-process proceedings.
Mr Colin Nicholls QC, for Mr Gilligan, had submitted that collusion between British and Irish police occurred after the arrest of Mr Gilligan at Heathrow Airport in October 1996 for alleged drugs offences.
A trial in England was put on file in September 1997 following a Crown Court ruling that precedence should be given to moves to return Mr Gilligan to Ireland.
Mr Nicholls alleged bad faith and "manipulation of the court process" to ensure that Mr Gilligan was held in custody while the extradition request was perfected. The allegation against Mr Gilligan was that he "procured the killing of Veronica Guerin by supplying to another person the means for that person to do the killing with the result that that person was killed".
Mr Nicholls argued that the Irish warrant was defective because the charge of murder specified on it did not correspond with the same offence defined in English law.
But Lord Browne Wilkinson and the four other law lords immediately announced that they were rejecting the arguments made on behalf of Mr Gilligan. They took the unusual step of giving an immediate decision because of the importance and urgency of the case.
Lord Browne Wilkinson said the High Court ruling against Mr Gilligan would be affirmed and his appeal dismissed.
The law lords also rejected a challenge against extradition in the case of Mr Edwin Ellis (42), who is charged with unlawful carnal knowledge of an under-age girl in Co Clare. Both cases had been brought together because they raised similar legal issues relating to "correspondence of charges" in Irish and English law.