According to Clean Green Cars, the Italian car maker has average CO2 emissions of 113g/km – significantly less than the industry average of 133g/km.
This compares favourably to the most polluting manufacturer, Porsche, which still sits above 201g/km because of its selection of high-performance sports cars.
Fiat has finished ahead of Toyota, Lexus and Citroen in the list despite its three rivals offering a selection of hybrid and electric cars in the UK.
However, Fiat’s range of small cars using efficient petrol and diesel engines outperforms its alternative-fuelled rivals when it comes to CO2 emissions.
Cars such as the new Fiat 500, the retro, premium city car that is a regular in the UK’s top ten best-selling cars, have helped Fiat take top spot once again in the charts.
The Fiat 500’s most important new engine is the TwinAir petrol, a unique two-cylinder, 0.9-litre unit delivering sub-100g/km of CO2 emissions.
Despite this, the engine delivers the same power as a much larger engine to ensure the Fiat 500 is not underpowered.
The other small car in Fiat’s range, the Fiat Punto Evo hatchback, has received an update for 2012 and as a result has contributed to an improvement of 3.29 per cent over the past 12 months for Fiat.
The introduction of the TwinAir engine to Fiat’s sister brand, Alfa Romeo, has ensured it too has recorded a green improvement, bringing emissions down from 129g/km to 124g/km on average.
The Alfa Romeo MiTo TwinAir model was launched this year, adding frugal petrol power to the stylish city car to complement the MultiJet diesels in the range.
The Fiat 500 TwinAir and the Alfa Romeo MiTo TwinAir, two of the greenest petrol cars on the market today, are available from Perrys Fiat dealerships and Perrys Alfa Romeo dealerships respectively.