Trade valuations experts at CAP are including CO2 data in the Black Book for the first time from May.

The publisher has taken the decision to help used car dealers be more aware of CO2 emissions bands as consumers are expected to be put off some vehicles by the consequent VED costs.

Mark Norman, operational development manager, said: “We have now introduced CO2 figures into Black Book because we believe that VED rates will become as influential on consumer choice as fuel economy and insurance costs. Dealers should get into the habit now of taking into account the likely VED bands of cars they acquire because the new rules will apply to all cars registered from March 2001.

"Depending on the speed of growing consumer awareness, this means that there is already an increased risk that many older, low-value cars will become less desirable to customers."

He suggested that cars emitting above 180 grammes of CO2 per kilometre will 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.