Leasing firm Alphabet has issued the warning after research showed that 80% of company car drivers want to reduce their tax bills when they next change their company car, by either picking a lower emission car or opting for a cash for car scheme.
Although most drivers intend to take the low emission car option, research by Alphabet shows many drivers will decide to 'opt out' and take the cash instead.
The firm's managing director Mike Baldry warned companies could stumble into problems if employees opting out of company cars were not 'led by the hand'.
He said: 'The problem with cash and personal motoring schemes is that they leave the employer with little control over the type of cars drivers use, how they are maintained and insured or when they are renewed.'
He claimed Alphabet's structured scheme, the Employee Car Ownership Plan, offered a better alternative, delivering cost savings by moving drivers out of company cars, while retaining a level of employer control over maintenance and the type of vehicles driven.
Baldry added: 'This would still leave the overall integrity of the fleet intact and for drivers, it would deliver a company car style experience, where everything from insurance to tyres is included.'