What’s new?The 5 is an excellent car — our favourite mid-sized MPV, in fact — and now diesel versions are arriving in the UK.There are two flavours of 2.0-litre engine: 108bhp on TS models (from £15,900) and 141bhp on Sport models (from £17,900). We’ve driven the top-spec Sport Nav variant, which gets satellite navigation and a DVD player, and comes in at just under £20k.You’ll know the engine from the Ford Focus C-Max, which also lends the Mazda its chassis.Do the changes work?Indeed they do. There’s nothing wrong with the 5’s petrol engines, but the diesel offers better cruising economy and comfort.The 143bhp unit is a little louder than the 108bhp version and less linear in its power delivery. But it’s still very driveable: response is respectable from low revs and particularly good above 2000rpm, aided by a six-speed manual gearbox (petrol models only get a five-speeder).At part-throttle at motorway speeds the engine is inaudible, while performance at the pumps — an average of 44.9mpg — is very good.Should I buy one?If you do a lot of miles, absolutely. The diesel isn’t as quiet as the petrol 5 around town, but it’s an entertaining steer and the improved economy and fine high-speed refinement mean it’s the 5 we’d have.