An official audit of Garda payroll found evidence that some officers were paid for performing duties at different locations at the same time.
The report also said the health and safety of both officers and the public were placed at “significant risk” because of how many hours some gardaí were working.
It found more than 1,050 cases where a garda had more than 16 hours’ duty over the course of a continuous 24-hour period.
A case where time and attendance were reported by one person at the Three Arena, on a major Garda operation, and for processing files at the same time was also raised in the report.
It said concerns about “the level of work in some cases” had been passed to Garda Internal Affairs and was under investigation.
The audit also listed a case where an officer had performed 75.25 hours over a period of 80.5 hours. It said “Herculean levels of duty” like that were questionable on health and safety grounds.
The garda audit, which was finalised last November, has been released under Freedom of Information and covers the calendar year 2018 when the bill for “extra duty” was €117 million. The audit said improvements had since been made but that the findings were a matter of considerable concern.
The findings came from the Garda Internal Audit Service which carried out an examination of Garda members who had reported the highest levels of duty.
It detected nine cases where members with a combined total of 124 hours of service were reported to be on duty in two places at the same time.
The report said this was of “significant audit concern” and that the existing manual system of time sheets did not allow for those incidents to be easily discovered.
The audit also found more than 23,000 hours of regular duty – the equivalent of 590 working weeks of 39 hours – where the Garda member involved was supposed to be on a period of “designated rest”.
It said while “exceptional circumstances” might occur due to Garda operations, management were obliged to ensure officers did not breach working time agreements.
Public duties were also performed by officers on annual leave, or time off in lieu, in cases covering around 160 hours, the audit found.
It said this should not have been happening and that attendance of gardaí should not be required while on holiday or on time off.
Garda management said this was not always possible due to the “exigencies of the service” if nobody else was available.