The Garda Ombudsman said it was investigating an allegation that a Garda whistleblower was followed by an unmarked garda car while attending a confidential meeting with GSOC, according to correspondence seen by RTÉ's This Week.

The alleged surveillance occurred when Garda whistleblower Keith Harrison travelled from Donegal to Galway to attend a meeting with the Garda Síochána Ombudsman Commission (GSOC) in March of this year.

The meeting was held to discuss developments in Garda Harrison's case, which is being investigated by GSOC.

He alleges that his career was ruined by harassment and unwarranted disciplinary inquiries after he arrested a colleague for suspected drink-driving in 2009.

Following the meeting, Garda Harrison alleged that his own private car was followed by an unmarked garda car, which he claimed to have recognised as having been one of several which make regular drives past his Donegal home.

It is understood that GSOC has taken the allegation seriously that a whistleblower might be placed under surveillance while travelling to attend a meeting with GSOC.

It is understood that a senior inspector at GSOC informed Garda Harrison's lawyers in March that they were examining the allegation.

Documents seen by RTÉ's This Week show that the meeting between two officials from GSOC, including the senior inspector, was organised with strict secrecy.

The venue was selected a considerable distance away from where the whistleblower lived and GSOC's Dublin HQ.

It was booked to take place in a hotel meeting room in Galway and the booking was made via a private travel company and none of the participant's real names were used, RTÉ's This Week understands.

In total, only four people were supposed to be aware that the meeting was taking place.

One of Garda Harrison's long-standing allegations, which have been with GSOC for two years, is that his home in Donegal has been subject to unwarranted garda surveillance with cars driving past, both marked and unmarked, and he has kept records of the particular garda cars involved.

Garda Harrison declined to comment.

GSOC would not say what response they received, if any, from gardaí in relation to the allegation or whether the issue had been resolved or was still ongoing.

Responding to a query from RTÉ's This Week, a spokesperson for GSOC said that they "cannot, for confidentiality reasons, discuss the detail of an investigation that may be under way as a result of a disclosure made to GSOC under the Protected Disclosures Act".

Similarly, the garda press office said that the force was "precluded from commenting on protected disclosures".

"Without discussing any individual, An Garda Síochána seeks to ensure any employee of An Garda Síochána who raises issues will be fully supported. In this regard, Protected Disclosure Managers have been recently appointed to liaise directly with employees making protected disclosures, and we are working with external experts in this area to help ensure that anyone speaking up is supported and protected in An Garda Síochána," the garda statement added.