The error and its handling are revealed in an internal audit of the payroll office which handles salaries for staff in the HSE’s Dublin-Mid-Leinster and Dublin-North East regions.

Some 1,144 overpayments were reviewed during the audit — 76 a year over 15 years — with 6% of staff in the region being overpaid to some extent.

While some repaid the money and others are in the process of doing so, a total of €2.5m in salary overpayments remains outstanding. The auditors indicate that most of it will never be recouped.

Just five cases have been forwarded to the HSE legal department to be pursued through the civil courts, but they involve amounts ranging from €329 to €6,500.

In total, 41 overpayments were of amounts of €10,000 or more, the worst being:

- €191,225 to an employee in an unspecified position who continued to receive full pay while on reduced hours from 2002 up to their retirement in 2010. A repayment schedule of 3% of the pension was agreed but the audit states: “According to this repayment schedule, it will take approximately 561 years to fully repay the amount.” It said the repayment deal amounted to a “de facto write-off”;

- €85,865 to a medical scientist from 1999 to 2003 when he was paid for working full hours even though he was out sick. His sick leave had expired so he was due no pay. The possibility of legal action through the civil courts is being examined but the case is not yet with the HSE legal department:

- €55,529 to an employee whose hours were reduced but whose salary was not. The audit says repayment has commenced;

- €46,373 to an employee who resigned in October 2008 but continued being paid until June 2009. The audit says the money is being repaid;

- €34,373 to a woman who continued to be paid while taking unpaid leave, parental leave, and a career break after her maternity leave. The audit says that repayment is “due to commence”;

- €33,841 overpaid to a staff nurse who was wrongly paid as a public health nurse. The overpayment was written off after the intervention of the Labour Relations Commission.

The audit identifies that the main reasons for overpayments are late notification to the payroll department of resignations, deaths, and reduction in hours, as well as employees being placed on the wrong point in the salary scale and “clerical errors”.

It also found that only half the cases had complete documentation and correspondence detailing what had happened and what action was being taken. One in five cases had no documentation whatsoever.

The auditors recommend that all employees and managers be made aware of their responsibilities to ensure overpayments do not occur and what they should do when they do happen. It was noted that only 37% of employees had got in touch with the payroll department when they were overpaid.

The audit notes that the payroll manager had accepted the contents of the report and its recommendations.