An investigation by consumer rights publication Which? is highlighting the cost of diesel cars verses petrol.

This year is set to be the first in which diesel cars will make up more than half the new car market. The type of fuel customers will go for should be driven by what their annual mileage is and the majority of dealers will be helping customers to make the right decision.

Which? tested identical-spec petrol and diesel versions of the Ford Fiesta, Vauxhall Astra, Volkswagen Tiguan, Volkswagen Sharan, BMW 5 Series, and Peugeot 308 SW.

It calculated the annual fuel bill for each based on a mileage of 10,672 (the average annual mileage in the 2012 Which? Car Survey).

Which? believes it could take up to 14 years to recoup the upfront costs in fuel savings on a diesel.

Richard Lloyd, Which? executive director, said: “Fuel price rises have been hitting household budgets hard, so it’s important that consumers know they are getting value for money when they buy a car.

“Diesel cars are known for their fuel efficiency, but with lower pump prices for petrol and a premium price tag for diesel cars, it may make more financial sense for families to go for the petrol version."