Chairperson of the Garda Ombudsman Judge Mary Ellen Ring has told the Minister for Justice that the Ombudsman's use of serving gardaí to assist them with a major criminal investigation would impact on the Ombudsman's perceived independence from the force.

The warning is made in a copy of a letter obtained under the Freedom of Information Act by RTÉ's This Week.

In the letter, Judge Mary Ellen Ring told Justice Minister Charlie Flanagan earlier this year that the impact of combining garda members with GSOC personnel, as part of the ongoing high-profile criminal investigation into alleged fraud at the Garda College in Templemore, could "cast a shadow over independent oversight of the gardai".

She went on to say that GSOC were considering taking the step of carrying out an external review to confirm that their own probe was carried out independently.

The Templemore investigation is one of the largest undertaken by GSOC - and it arose after a dossier was forwarded to GSOC by the former Garda Commissioner Noirin O'Sullivan in 2017, following prolongued public controversy and sustained questioning by the Dail's Public Accounts Committee.

The judge told the minister that there was "no doubt that issues arise with the public perception" of combining serving gardai and GSOC investigators.

However, she said she had every reason to believe that the serving gardai who were working alongside her own team would act in a professional manner.

GSOC has repeatedly complained that they have insufficient staff to conduct the work required of them under law. 

They used a section of the garda Siochana Act 2005 to appoint a number of serving gardai to their investigative team, in a case where they lacked the capacity or special skills required for a particular case. GSOC said it was the first time in their eleven year history they had to use this measure.

Asked if they had any further comment to make on the letter this week, GSOC told RTÉ that they had no doubts about the professionalism of the gardai working with them on this investigation.

However, the statement went on to say that GSOC was hopeful that the Commission on Future of Policing -- which is to to make recommendations on policing in Ireland in the coming week -- will, to quote..."reinforce the importance of independent oversight and the need for such oversight to not need to resort to Garda assistance for investigations". 

The statement went on to say that "support therefore is not just solely financial but also greater powers to enable GSOC to do independent investigations".

A spokesman for Minister Charlie Flanagan said the Minister was acutely aware of the importance of GSOC's work but added that he is very conscious that the Commission on the Future of Policing is due to report imminently. They said it was likely the Commission would propose far reaching legislative changes -- relating to these matters.

They also said that GSOC's budget would rise by an extra €400,000 this year and there was plans to increase their manpower.