Mechanically nothing — the 318d is identical to the 320d, only its 2.0-litre turbodiesel has been detuned from 161bhp to 121bhp and is it £1110 cheaper.
Do the changes work?
Unsurprisingly, it’s a lot like a 320d, only slower. The engine is smooth and quiet, but there is a little vibration through the pedals. It drives through a slick six-speed manual gearbox, which is long legged for economy, but necessitates the odd downchange when you want a burst of acceleration.
Should I buy one?
Maybe, although £22,215 is quite a lot of money for a car with only 121bhp. That said, it’ll hit 129mph, go from 0-62mph in 10.1sec and its equipment levels are class-competitive. Perhaps the fact that it only emits 150g/km of CO2 may prove the most persuasive point.