Britain's cleanest cars - Compact executives

What Car? Greenest Compact Executive: Saab 9-3 1.9 TiD 120

The diesel version of the Saab 9-3 is so good on CO2 emissions that it equals the output of the Ford Ka city car.

The saloon version is rated at just 147g/km – closely followed by the estate – and returns a combined 52.3mpg. Get out of town and the official figure rises to 64mpg.

There is, however, one more laurel in the 9-3's environmental crown: the 120bhp diesel and more powerful 148bhp version come with a particulate filter. This maintenance-free trap so thoroughly eliminates soot from the tailpipe emissions that the 9-3's particulate figure is officially recorded as 0.000g/km.

The Saab may not match the driver appeal of a BMW 3 Series or Mercedes C-Class, but the 1.9 TiD has them licked on green performance.
Price: From £19,460
MPG: 52.3
CO2 emissions: 147g/km

BMW 318d
The least powerful diesel 3 Series is close behind the Saab on CO2 and mpg. To win a place here, though, it must be fitted with the optional £415 particulate filter. Same goes for the 320d, but the 330d has one as standard.
Price: From £22,530
MPG: 50.4
CO2 emissions: 150g/km

Volvo S60 2.4 CNG
Volvo's dual-fuel saloon runs on either petrol or compressed natural gas (CNG).

Use CNG and the CO2 drops from 208g/km to 159g/km. It's cleaner on local emissions, too, halving the carbon monoxide output.

Finding a garage with gas is the only problem, but you'll be exempt from London's Congestion Charge and a discount puts it in the lowest band for company car tax. You can choose between models that run on CNG or liquefied petroleum gas (LPG).
Price: From £22,460
MPG: 31.7
C02 emissions: 159g/km
Exempt from London Congestion Charge