The cheaper option is not always a diesel engine

DIESEL cars may be only marginally more economical to run than petrol-powered models, a survey has revealed.

An investigation by a motoring magazine discovered that some popular diesel cars have to be driven more than 32,000 miles a year before they become more cost-efficient than their petrol counterparts.

Diesel vehicles now account for more than half of all motors sold in Britain.However, as petrol engines become more efficient, new research explodes the myth that diesel is always the cheaper choice.

Auto Express magazine found when depreciation, road tax and fuel bills are taken into account, many diesel cars are less efficient than petrol models.

For example, a city-friendly diesel Fiat 500, below, would have to be driven 32,202 miles a year over three years before it becomes cheaper than the same petrol model. This is because it is 2,400 more to buy new, does only 14 miles per gallon more than the petrol version and depreciates more over three years.

A magazine spokesman said: "The only way to ensure you're buying the most frugal new model for you is to do the sums carefully."