Petrol or diesel: which should you buy? - Impact on environment: diesel wins

Diesel-run cars are considered to be more environmentally friendly than petrol equivalents because they emit around 20% less carbon dioxide than petrol engines.

They are more efficient and offer better fuel economy. If all models sold in the UK are taken into account, petrol cars emit an average of 172.2g/km of carbon dioxide, compared with the average diesel carbon dioxide emissions figure of 165g/km.

Diesel is not a particularly clean technology, though. Diesel engines emit more particulates and nitrous oxide than petrol equivalents.

Black carbon emissions associated with diesel vehicles contribute to global warming effects, although the magnitude of these effects is still uncertain.

Diesel particulate filters will stem black carbon emissions, but only about 50% of new cars sold in the UK are fitted with filters.