A High Court judge has reserved his decision until tomorrow on an application ultimately aimed at blocking the PSNI's Deputy Chief Constable, Drew Harris, from taking up his position as the next Garda Commissioner.

Belfast-based researcher Ciaran MacAirt, whose grandmother Kathleen Irvine was one of 15 people killed when a loyalist bomb exploded at McGurk's Bar in Belfast in December 1971, has asked the High Court to judicially review the Government's decision to appoint Mr Harris.

The PSNI deputy became the first Garda Commissioner appointed from outside the Republic of Ireland when he was announced for the role in June.

The State, represented by Remy Farrell SC, has opposed the application, and argues Mr MacAirt's action is "unstateable and novel" and should be dismissed.

Following the conclusion of submissions from both sides, Mr Justice Denis McDonald said he was reserving his position on whether to grant permission allowing Mr MacAirt's case to be heard at a full hearing of the High Court.

The judge, who acknowledged the urgency in the matter as Mr Harris is due to commence the role on 3 September, said he hoped to be in a position to deliver judgment tomorrow morning.

In proceedings against the Minister for Justice, Ireland and the Attorney General, Mr McAirt seeks various orders, including one quashing the decision to appoint Mr Harris as Commissioner of An Garda Síochána and a declaration that he is unsuitable for the post.

In the alternative, he seeks an order preventing Mr Harris having any role in the direction and control of the garda investigation into the murder of Irish citizens where there is credible evidence of collusion by the RUC or other agencies of the British state in the murder.

He also seeks declarations that the Irish State is obliged to conduct independent investigations into murders of Irish citizens where there is credible evidence of collusion with the British security forces.

He further seeks a declaration that due to his obligations under the UK's Official Secrets Act and his role in the protection of the PSNI, the RUC and other agencies of the UK, Mr Harris would be incapable of controlling an independent investigation into the murder of those Irish citizens where collusion was alleged.

Mr Farrell for the State said that the case being advanced by Mr MacAirt was "unstateable" and even when taken at its height was "nothing more than an expression of an opinion" that the applicant does not agree with Mr Harris's appointment.  

No legal points had been raised in the action that would allow the court grant Mr McAirt permission to bring his challenge before a full hearing of the court, which was being asked to substitute Mr McAirt's views over those of Police Authority, which had recommended his appointment.

Mr Farrell also told the court that the Government had a minimal role in Mr Harris's appointment. Mr Harris had been selected following a process undertaken by the Police Authority and the Public Appointments Service.

He said Mr MacAirt had not challenged that process nor did he make the argument that the decision to nominate Mr Harris was irrational and unreasonable or that there was a flaw in the process.

Mr Farrell said that the recruitment process for the new Garda Commissioner had also sought candidates from outside the State. Obligations of such candidates from other countries, under laws such as the UK's Official Secrets Act had been taken into account by those undertaking the search for a new commissioner.

The State's submissions were rejected by barrister Gerard Humphreys who appeared for Mr MacAirt with Ruadhan MacAodhain of McGeehin Toale Solicitors.

Ciaran MacAirt (centre) outside court today

Mr Humphreys said Mr Harris lacked the independence required to be Garda Commissioner due to his role in the PSNI and its predecessor the RUC.

He said Hr Harris could not direct or control any garda investigation into the murder of an Irish citizen where there was credible evidence of collusion, between the killers and the RUC or agencies of the British state, including the Dublin and Monaghan bombings.

Due to his senior role with the PSNI, and contacts with other agencies of the British state including MI5, Mr Harris has possession of information directly relevant to garda investigations into the murder of Irish citizens during the troubles.

Mr Humphreys said Mr Harris had signed and was bound by the UK's Official Secrets Act making it impossible to fully discharge his duties as the next Garda Commissioner. This conflict was incompatible with the duties of commissioner as laid out under Section 5 of the Garda Síochána Act, in particular to State security and the investigation of crime. 

Mr MacAirt, who says he was shocked by the decision to appoint Mr Harris, had written a book about the McGurk's bombing and is a director of the Charity Paper Trail, which supports victims and survivors of the Troubles. He claims that he has been trying to establish the truth behind the bombing.

The RUC initially blamed it on an IRA bomb being accidentally detonated when in fact the bomb was deliberately planted in the bar by the UVF. Mr MacAirt claimed there was never a proper investigation into the bombing, and alleged there was an RUC cover-up into what happened.

He claims his efforts to find the truth had been frustrated by the PSNI and he had been consistently obstructed by Deputy Chief Constable Harris.

He alleges that as part of his role with the PSNI Mr Harris had responsibility for the PSNI's Historical Enquiries Team, which investigated the bombing. It had produced four reports, which Mr McAirt claimed Mr Harris had the final say over.

Those reports had all been rejected by the victims of the bombing because allegations of collusion between loyalist paramilitaries and the RUC had not been addressed.