FLEET managers must take action to stop company car drivers loading extras on to their vehicles, at massive expense to employers and which are practically worthless within months. Drivers who are given a basic allowance to spend on a vehicle without strict guidelines can be tempted to spend every last penny by adding extras, from leather steering wheel to CD players.

A new residual values guide for options and extras from Glass's Guide reveals that, although drivers may feel they have spent their allowance well, the true cost of their choice will become clear at disposal time. Although some extras achieve acceptable values - albeit still a fraction of their new price - some are branded 'benefit', indicating that they are worthless although they will increase the chances of a car selling compared to a model without that particular option.

Bill Carter, editor of Glass's Information Services' residual value forecasting product AutoProVision, said: 'The original cost of the extra does not reflect its second-hand value. Fleet managers must be very wary of the options their drivers put on. Satellite navigation is the best example because it is a high-cost option, yet is worth very little on sale.' And Mark Norman, editor of CAP Monitor, said: 'Extras are a minefield. Some are worthwhile but, if a fleet driver spends more than £1,000 on satellite navigation, a private user who wants a car to go to the shops and on holiday will not put as much value on it.'