Inevitably, the answer here is ‘it depends’. Petrol cars tend to be cheaper to buy and put out fewer harmful NOx emissions than diesel cars, but they can’t quite match the sky-high mpg figures diesel cars can achieve.
In practice, petrol will usually be a better choice if you mostly drive short to medium distances thanks to its greater affordability – you’ll also likely find more choices with petrol engines, as diesel options are becoming more limited over time.
Long-distance drivers may still want to consider a diesel, however. This is because the higher average mpg figure will outweigh the extra purchase price compared to a petrol model. What’s more, long-distance drivers will avoid the DPF issues that afflict diesel cars mainly used for shorter journeys.