What Car? Q&A - Petrol or diesel?

Q: I want to buy a new five-door Ford Focus 1.6 Style. I do about 5000 miles a year, and will be keeping the car for about three years. Which will be cheaper – petrol or diesel?
Bob Barnes

A: Even though your mileage is low, a diesel Focus will probably work out cheaper in the long run – but perhaps not for the reason you're thinking.

Like most diesels, the Focus 1.6 TDCi uses less fuel than the equivalent petrol version. However, based on current pump prices, you'd have to cover more than 46,000 miles just to break even – and that would take you over nine years.

There's more than fuel to think about, though. Diesel Focuses command a higher price on the used market, so you'll get more cash back when you sell it after three years.

You'll also save £110 a year on car tax, because of the diesel model's lower carbon dioxide (CO2) output. Add these savings together and the 1.6 TDCi 90 should work out around £630 cheaper over three years. If you were to go for the more powerful (110) version, the likely overall saving drops to £470.