Six dissident Republicans who were serving lengthy prison sentences for bombing offences in the UK have been released from Portlaoise Prison after they launched High Court challenges against the legality of their detention.

The six are brothers Aiden, 37, and Robert Hulme, 34,  Darren Mulholland, 34, James McCormack ,47, Anthony Hyland, 41, and Liam Grogan, 36, who claimed they were entitled to immediate release due to significant differences between the sentencing systems in Ireland and the UK contained  in a recent Supreme Court judgment.

The six were convicted and jailed for 20 years or more by the British courts in the late 1990s and early 2000s.

They were transferred back to Ireland to serve out the remainder of their sentences.

They were not entitled to early release under the Good Friday Agreement due to their links to dissident republicanism.  They had release dates varying from September of this year to early 2016.

The six applied to the High Court for inquiries, under Articles 40.4.2 of the Irish Constitution, into the legality of their continued detention, which they argued was unlawful.

In what were seen as test cases inquiries sought by Liam Grogan, represented by Michael Ó Higgins SC and Darren Mulholland, represented by John Alymer SC, came before Mr Justice Gerard Hogan.

It was argued that both men had fully served the sentence imposed on them in England, that their continued detention was unlawful.

They also claimed that had the standard Irish remission rates of 25% been applied they would have been due for release some time ago. The state did not contest the applications.

After being informed of the facts of the case the Judge made declarations that their detention was unconstitutional and ordered their immediate release.

Applications for inquires brought by the remaining four applicants were adjourned. When the matter returned before Mr Justice Hogan the court was informed the Hulme brothers, McCormack and Hyland were released and the application for an inquiry was now moot.

Inquiries into the detention of three more dissident republicans, who raise similar arguments, are due before the High Court next week.

In their proceedings the men argued the Irish State was enforcing sentences imposed by the English courts that are not compatible with Irish laws. 

Under English law the men were entitled to be released after serving the bulk of their prison terms before being released on license into the community to serve the remainder of their sentence. None of the men had been released as there is no provision in Irish law to be released on license, it was argued.

The men's lawyers claimed the state's position was that all six should remain in prison for the full duration of their sentences.

Their lawyers said the state's position was unlawful. The men had completed their sentences and were entitled to be released, they claimed.

It was also argued that a recent Supreme Court judgment in an action brought by Sligo man Vincent Sweeney, which highlighted significant differences between the sentencing systems in Ireland and the UK, and the position adopted by the State in a number of other similar cases in relation to transferred prisoners supported their case for immediate release.

The case of Sweeney, whose immediate release was ordered by the Supreme court, illustrated that a person is entitled to release when they have served the period of imprisonment compatible with the true nature of the sentence imposed on them in the sentencing state.

It was also argued sentences of more than 20 years, imposed on some of the men, are incompatible with Irish law.

This is because the terms exceeded the maximum sentence permissible in Ireland for a similar offence. 20 years is the maximum sentence a person convicted of similar explosives charges can receive under Irish law.

In 1999 Hyland, Mulholland and Grogan were convicted at the Old Bailey London of conspiring to cause explosions in the UK between June and July of 1998.

The trial heard they were part of a Real IRA gang that plotted to use the explosive semtex and incendiary devices to cause explosions in London. 

Hyland, from Mount Tallant, Terenure Dublin was sentenced to 25 years in prison, while Mulholland, Meadow Grove Dundalk and Grogan Lakelands, Naas, Co Kildare were jailed for 22 years. They transferred to Ireland in 2000.

In 2003 the Hulme brothers, from Dundalk in Co Louth, and James McCormack, also from Co Louth, were convicted following their trial at the Old Bailey of conspiring to cause explosions likely to endanger life and possessing explosions. Their trial heard the men, who were arrested in 2001, were also members of the Real IRA.

They were convicted in relation to a bomb attack outside the BBC television centre in Shepherd's Bush, London in March 2001. They were also convicted in relation to bombings of Ealing Broadway tube station in London in August 2001 and Smallbrook, Queensway, Birmingham, the following November. 

The Hulmes were sentenced to 20 years in prison, while McCormack received a 22 year sentence. Their transfer to Portlaoise occurred in 2006.