Auditors “cannot rule out” a school improvement service allowed staff to boost travel expenses by changing their office location.
Rules changed to let Gwynedd Council workers only claim for travel beyond the distance between home and work.
But an audit found GwE let staff choose the nearest office as their official workplace, lowering the starting point for mileage claims.
A GwE spokesperson said the policy change had been reviewed.
While the council’s decision to change the rules was aimed at saving around £290,000 a year, GwE – which is funded by local authorities in north Wales – saw its expenditure increase between 2017 and 2019, according to the Local Democracy Reporting Service.
Auditors also found mileage claims were not being checked properly, leading to an 800-mile claim submitted for an 80-mile journey.
The audit report said a number of staff had changed their official work location to the office nearest their homes.
“A number of staff had wished to change their official work location to the nearest offices to their homes,” it said.
“The fact that this may have happened in response to the change in policy and the effect this has on officers’ travel costs cannot be ruled out.
“It appears that those who have changed their official work location have benefited financially, whether by claiming for the journeys they make to their usual place of work, or by reducing the loss associated with the distance from home to their official work location – or a combination of both.
“To this end, Internal Audit cannot provide assurance that value for money has been taken into account when changing work locations.”
A spokesperson for GwE said it had worked closely with the relevant officers at Gwynedd Council and the directors of education of the six authorities across north Wales to “secure agreement that the regional service remained effective and efficient”.
“Following the policy change GwE staff are not claiming travel costs from their homes,” they added.