Britain's cleanest cars - Superminis

What Car? Greenest Supermini: Toyota Aygo

No other new car on sale in the UK will travel farther on a gallon of fuel.

According to official economy figures, the Toyota Aygo 1.4 diesel (and its sister car, the Citroen C1 1.4 HDI) returns 68.9mpg on the combined cycle – and this stretches to a parsimonious 83mpg out of town.

The three- or five-door city car also posts the UK's second-lowest CO2 emissions of just 109g/km – not far behind the ultra-clean Toyota Prius hybrid, which costs twice as much.

Although the diesel Aygo is £1100 dearer than the equivalent petrol version, you'll appreciate the extra pulling power. We also reckon its negligible thirst and clean emissions make this one of the greenest small cars on the planet.
Price: From £8330
MPG: 68.9g
CO2 emissions: 109g/km

Smart Fortwo
The tiny two-seater is one of the most frugal non-hybrid petrol cars.

Its 60mpg combined economy helps explain an ultra-low CO2 output of 113g/km – perhaps not that surprising, with a 0.7-litre engine calling the shots.
Price: From £6775
MPG: 60.1
CO2 emissions: 113g/km

Citroen C3 1.4 Stop & Start
This clever version of Citroen's C3 supermini cuts the engine automatically when the car is stationary to save fuel. As a result, its urban economy is boosted to 41mpg.

The stop-start process is undemanding: the C3 replaces the regular starter motor with a beefed-up alternator that provides the power to restart the engine the moment you brush the accelerator to set off.

Once you've adapted to the silence at standstill, you'll wonder why all cars don't cut out at traffic lights.
Price: From £11,590
MPG: 49.6
CO2 emissions: 135g/km