Almost all fleet managers risk having claims turned down because they do not check private cars driven on company business.
The RAC found that only 2% of fleet managers checked to see if private cars used by company employees for work journeys were safe to drive, even though these cars were usually much older than company cars and were serviced less often.
RAC corporate services managing director Simon Cashmore said: "More than half of all fleet managers believe, incorrectly, that insurance policies for private cars cover work trips."
More than 11 million employees drive on company business every year.
