A garda believed to have given information to a senior figure in the Continuity IRA resigned from the force earlier this year after an internal inquiry into the incident.
The female garda had been stationed in Leinster.
Gardaí began the inquiry after they suspected she had texted the dissident republican the names of two men who had been arrested in connection with the discovery of a homemade bomb.
Gardaí intercepted the device and the Army Bomb Disposal Team was called in to make it safe.
The garda was interviewed about the suspected disclosure of confidential information and subsequently resigned but the incident is still the subject of a criminal investigation.
She had been associating with a member of the Continuity IRA who is well known to gardaí and the PSNI.
He has a number of previous convictions and served a lengthy jail sentence for explosives offences.
The internal investigation is understood to have established that the garda discovered the names of two people who were being detained in a garda station and how long they were to be questioned for and passed that information on to her associate in the Continuity IRA.
Garda sources say they became aware of this information through their own intelligence, not through MI5 or the PSNI, and immediately began an internal investigation.
However the UK and British security services are now aware of the matter.
Senior gardaí do not believe that the female garda, who has less than ten years service in the force, had access to high-level confidential information.
She is also currently the subject of a separate criminal investigation following an alleged assault earlier this year.
The interim Garda Commissioner is finalising a report on the matter for the Minister for Justice.