The cost was due to the vehicles being mistakenly ordered with steel rather than alloy wheels.

An East of England Ambulance Service spokesperson said: ‘We have retrofitted alloy wheels to some of our ambulances as they were not included in the original procurement due to an error. There is no additional cost than if the wheels had been fitted before delivery.

‘This work will be done in a phased approach so that we always have the appropriate number of vehicles to serve our patients.'

EAST said many vehicles in its fleet had steel wheels and there was no suggestion these cannot withstand 999 response driving conditions.

The trust added the retrofit was already budgeted for in its procurement order so there was no additional cost.

It said all future deliveries of new ambulances in 2025 will already be fitted with alloy wheels.

Unison East of England ambulance branch secretary Glenn Carrington said: ‘Demand on services is already far too high, so having fewer ambulances on the roads can be a serious problem. It leads to longer waiting times and puts patients at greater risk as their conditions could deteriorate.

‘Fixing the problem should not be at the expense of overtime payments that many staff rely on to supplement their income.

 ‘Maintaining a reliable, road-ready fleet is absolutely critical.'

Donna Thomas, GMB regional organiser, said: ‘This embarrassing and avoidable error shows a lack of due diligence and proper processes in EEAST.

‘Vehicles were unable to enter frontline service due to management mistakes – yet another delay to frontline response.

‘This is a trust which is currently subject to an improvement notice from the CQC, due in part to C2 ambulance response times.

'It has also removed 21 private ambulances from frontline service and announced plans to shut an emergency call centre in Bedford due to financial constraints.

'The money spent on this retrofit should have been used to fund clinical staff on the road. There must be accountability for this error.'