GAS-guzzlers will retain their values and popularity with senior executives despite the prospect of price increases hitting their secondhand values. With fuel prices predicted to be as much as 25% higher in three years' time, the leading price guides are divided over future residual values of thirsty executive vehicles and 4x4s.

Chancellor Gordon Brown accelerated the rate of fuel duty increases to which the UK is committed under its Earth Summit agreements in the Budget, giving a clear indication of the future direction of fuel prices. The executive market has however contracted dramatically in recent years and used values - particularly on Mercedes, BMW and latterly Audi models - have hardened as supply tightens.

CAP said the increases would have little effect on used values in the executive sector, where drivers were most likely to have the means to absorb the fuel duty increases, although Glass's Guide predicted potential problems ahead for cars of 3.0 litres and over.

CAP chief economist Mark Cowling said the 18p a gallon Budget increase was more likely to affect the supermini sector, where buyers had to live within tighter budgets. Glass's ProVison editor Adrian Rushmore said: 'User-choosers will carry on buying the big cars, but the problems may arise when these come back to the used market. The people who buy them then are more cost-conscious.'