According to the findings, covering more than 73,000 vehicles and 400 companies, 49% of businesses failed to check the insurance of employees required to drive on company business.
The situation is further complicated by the growth of cash-for-car schemes, as drivers using private vehicles for business use will fall outside of company vehicle insurance schemes and may not have insured themselves properly.
The research by HSBC Vehicle Finance says the issues are multiplied because there is no standard definition of business use cover, which varies according to each individual insurer.
Further complications are caused when business use is limited just to the policyholder and not named drivers of a particular car.
Tim Holmes, head of HSBC Vehicle Finance, said: 'Any individual involved in a fatal accident while on company business in their private car without the correct insurance cover could expose that company to corporate manslaughter charges in the future.
'Checking insurance details is a labour intensive activity but not enough companies are undertaking this fundamental check. Insurance cover has its grey areas so it is vital that businesses give it careful attention, especially companies asking staff to use their private cars on company business.'