Two bin lorries and five vans owned by South Norfolk Council were driven for three months without MoTs - because of a typing error.
One of the vans was involved in an accident while it had no cover - and a member of staff has been suspended while council chiefs probe how the mistake was not picked up.
The MoTs on the seven vehicles, which serve the Ketteringham Depot, expired on May 31 and continued to be used on the road throughout the summer.
During this period, one of the five vans was involved in a collision with another vehicle, an incident which happened on the A146 in July.
The incident involved a sprinter van used by the council and a car, which occurred on Thursday, July 12 and saw parties involved requiring hospital treatment.
However, all seven vehicles are now off the road, after the error was discovered on Friday, August 31.
South Norfolk Council has since said the reason this had been allowed to happen was a typing error, which incorrectly indicated the certificates expired at the end of May 2019.
South Norfolk Council said: 'Our initial enquiries have shown a staff member incorrectly typed 2019 and not 2018 into the maintenance database as the renewal date for a small number of vehicles.
'Seven out of our fleet of 55 vehicles including light vans were affected and all of the refuse vehicles have passed their regular six-weekly safety inspections.
'As soon as we were made aware of the situation the vehicles were taken off the road and we immediately arranged for those vehicles to be booked in for MoTs.'
In the meantime, the council is to launch a full investigation into the incident and how it was not noticed sooner.
A council spokesman added: 'A staff member has been suspended pending a full investigation. Our Ketteringham depot has been in operation for 40 years serving the residents of South Norfolk and this unfortunate administrative error is not a reflection on the hard work and dedication of our bin crews.'
The spokesman added that the DVLA and the Department for Transport had been made aware.
All seven vehicles are awaiting new MoT inspections and will remain off the road until these have been carried out.
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