Porsche

As a pure performance brand, it’s no surprise Porsche hasn’t got great green credentials. But that doesn’t mean it isn’t trying to make its cars more efficient.

In the past year, the German firm has slashed CO2 emissions across its line-up by 10.6 per cent. Its new direct-injection petrol engines have helped achieve this, as has the seven-speed PDK twin-clutch gearbox that is an option on the Boxster, Cayman and 911.

Pick the new Panamera four-door and you get stop-start technology, while the Cayenne SUV now comes with a diesel engine which emits 244g/km – that’s 66g/km less than the standard petrol version.

However, the cleanest Porsches on offer are the entry-level Boxster and Cayman models. Fitted with the same 252bhp 2.9-litre flat-six units, they both push out 221g/km and deliver 30.1mpg at the pumps. Add the PDK transmission, and CO2 drops by 7g/km, while returns are boosted by 0.9mpg.

BEST ECO BUY: Boxster