Many employers do not have procedures in place to check if employees who use their own cars on business regularly maintain their vehicles.
Some 83% have no such procedures in place, while almost three-quarters (74%) do not ask employees for a valid MOT for their car, according to the Grey Fleet Report from fleet provider Arval.
As a result, as many as one-in-four vehicles, amounting to over one million cars, are potentially poorly-maintained and incorrectly insured, raising fears for driver safety.
The survey of more than 400 fleet managers also shows that less than a quarter (24%) of businesses conduct any form of risk assessment or driving training, while more than half (56%) have no procedures for reporting accidents in non-company provided cars.
Mark Bird, a superintendent in the Metropolitan Police Traffic Unit, said: "Businesses must face up to their duty-of-care responsibilities and realise that they are responsible for the welfare of their employees when on the road for business purposes, whether they are driving a company car or not. More and more, we carry out follow-up investigations with companies after collisions, to ensure that work-related road safety is embedded within company policies.""