The leading UK used car price guide, the CAP Black Book, is to start including CO2 emissions figures and related car tax bands in its listings.

CAP said the decision to include CO2 figures and tax bands was prompted by the potential impact on used car values caused by proposed annual ownership tax (vehicle excise duty) rates to be introduced next year.

CAP believes consumer awareness of the mounting cost of VED will lead to many older cars losing value more rapidly as buyers take into account the cost of taxing the vehicle.

Cars emitting above 180g of CO2 per kilometre are expected to be hardest hit, with the annual cost of a tax disc representing half or more of the car's trade value in some cases.

For example, a 2001 Y-registered Fiat Marea 150 20V ELX saloon is today valued in the trade at around £650. If next year's proposed VED rates are introduced, the Marea will cost £415 to tax for 12 months. If a consumer pays the estimated £1,225 retail value of the car and intends to keep it for three years, its taxation cost over time will be more than they paid for the car originally.