Three Garda officers under investigation over the improper quashing of penalty points had cleared more than 600 driving licences over a three-and-a-half year period, an internal inquiry has found.

A probe into the controversy by assistant commissioner John O’Mahony found the actions of the unnamed gardai may constitute a breach of Garda discipline rules.

The three were directly involved in wiping penalty points for drivers on 661 occasions between January 2009 and June 2012.

A further disciplinary investigation, to be headed up by assistant commissioner in charge of internal affairs Fintan Fanning, has been launched into these cases.

Justice minister Alan Shatter said many of the more serious allegations levelled against Garda officers had not been substantiated.

“I am relieved that no evidence has been found to suggest any criminality in the cancellation of fixed charge notices,” he said. “However, I am concerned that it appears that there have been cases where clearly laid out procedures for the cancellation of notices were not followed, for example where tickets were cancelled by some superintendents outside their Garda district areas.

“It also appears that, in some cases, detailed records were not maintained.”

Mr Shatter said the subjectivity involved in whether to grant a cancellation inevitably left room for disagreement on individual decisions. The justice minister has ordered Garda Commissioner Martin Callinan to tighten up rules around the quashing of penalty points without delay.

Minister for Transport Leo Varadkar, rejected an accusation by independent TD Mick Wallace that the report was a whitewash.

“I’ve read the report. It reassures me that I can be certain about the integrity of the penalty point system,” said Mr Varadkar.

Senior gardai have the power to terminate points when motorists write to them and outline exceptional circumstances that led to the points being incurred, such as speeding during a medical emergency.

However, while records are required to be kept during the termination of points in such cases, the investigation has found that those procedures were not followed in a large number of cases.

The names of all people who may have benefited and the gardai who terminated the points have been redacted from the report.

However, Garda sources said it had never been intended to publish names for fear of implying wrongdoing in cases where none had been proven.

Two whistleblowers within the Garda who gained access to the Pulse system claimed that the list of beneficiaries runs into tens of thousands and that view has been supported by a group of TDs who have campaigned on this issue, including Luke Ming Flanagan (Ind), who has since admitted that he benefitted from points being terminated from his licence.

Additional reporting: PA