Petrol or diesel: which should you buy? - Fuel savings v list price: petrol wins

So why go for diesel? Simple, diesel engines offer better fuel economy than petrol equivalents - but how much will you actually save?

Diesel cars may be cheaper on fuel, but they are more expensive to buy. Our research shows that you'll have to drive a lot of miles before your diesel motor starts to pay off.

However, it's unlikely you'll ever recoup the extra initial outlay if you are driving a small diesel car and doing low mileages.

For example, a Citroën C1 diesel may well deliver 7.5mpg more than the petrol equivalent, but the petrol is £1470 cheaper.

It means the owner of a C1 diesel doing 8000 miles a year will take 73 years to recoup that initial cost through savings on fuel.

The diesel choice makes more sense if you're doing more miles and drive a more luxurious car.

The Mercedes-Benz E220 CDi Classic is a wise buy compared with its petrol equivalent, the E200K Classic.

In this case it'll only take you two years to recoup the extra initial outlay in fuel if you drive 40,000 miles a year.

Car buyers looking for fantastic fuel economy might be tempted by the Volkswagen Polo Bluemotion, which goes on sale in the UK this month.

It offers an impressive combined fuel consumption of 72.4mpg, but it is £4410 more expensive than its petrol equivalent.