A woman, who claims to have witnessed a garda using a breathalyser machine on himself, has said she is concerned that dishonest practices will continue into the future.
The woman, who worked in a garda station for more than 25 years, has raised her concerns with the Road Safety Authority, garda management, and GSOC.
Speaking on RTÉ's This Week, she said she was working as a clerical officer in a station in January 2014 when she witnessed a garda falsifying a breath test.
She said: "The garda in question was sitting at a desk. I noticed the garda had an alcometer in his hand and was blowing full force into the alcometer.
She added: "I also noticed that he had a bundle of tubes in the other hand and a blank form in front of him. And I straight away questioned him as to what he was doing.
"His reply was ‘Oh, I'm just making up some numbers’. He looked embarrassed and I thought I caught him on the hop."
She said she automatically assumed that his reply meant that he was falsifying the data.
The woman said she brought the matter to the attention of senior gardaí at the station, and was invited to make a formal complaint but did not do so.
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She said falsifying breath tests by self-breathalysing would be impossible to detect under the current system.
"It is that my belief is that the figures given, as in the one and a half million, could be way worse because this method, if used, is totally undetectable," she said.
"Everything looks perfect on paper. If you breathalyse yourself using the alcometer, the alcometer will tally perfectly with the return, meaning that it's un-investigatable," she said.
An Garda Síochána said it is "determined to ensure that all the issues raised in relation to breath-tests are thoroughly addressed so they can't happen again".
The organisation is urging "anyone in the organisation - members and civilians - with information relating to breath tests issues or evidence of wrongdoing within An Garda Síochána to bring it forward to Assistant Commissioner [Michael] O'Sullivan and the Policing Authority who are conducting their own examination into the breath-test issue".
The woman also raised concerns that improvements in technology will not solve the problem.
"The new alcometers will have GPS attached to them that will record time and date to them as well - may not be enough to prevent falsification in the future, because if the gardaí are at the correct location, using the new technology, and if nobody is looking or if supervisors turn a blind eye to it, then falsification could continue into the future," she said.
The woman said she did not make a formal complaint, or a protected disclosure.
She also said that she is involved in a human resources process with garda management, after she made a complaint of bullying against the garda in question, and against three other members of the force working at the station.