The Italian manufacturer finished joint top of the table alongside Mini in new research into CO2 and other harmful emissions.
Clean Green Cars uses CO2 emissions data for each car manufacturer and weighs it against the different models sold to find an overall ‘environmental impact’ figure that is not affected by one particularly clean or dirty version of a car.
Richard Bremner, Editor of Clean Green Cars, said: “CO2 is hugely important, but it is not the whole story. A car that is good for CO2 can be bad for other pollutants and vice versa. We are the only organisation that has analysed the performance of every single car sold in the UK so far this year.”
Fiat achieved the lowest score courtesy of average CO2 emissions of 125g/km. The manufacturer also finished in the top five best performers in terms of Oxides of Nitrogen (NOx) and soot-like Particulates.
The final score was given as three – 4.3 less than third placed Suzuki and ten times lower than bottom-placed Jeep, which has average CO2 emissions of 223g/km.
Fiat achieved the top ranking because of its range of small cars such as the Fiat 500, Fiat Punto and Fiat Punto Evo. The lack of a larger MPV or saloon meant average emissions are much lower than other volume manufacturers.
Japanese manufacturer Mazda also performed well in the research by finishing fifth overall with a score of 10.7. Despite a slightly higher average CO2 of 147.6g/km, Mazda performed particularly well on the amount of NOx from its model range.
Mazda’s average CO2 emissions are expected to fall once new, more efficient engines are introduced to the Mazda2 supermini and Mazda3 ranges.
Elsewhere, despite an improvement of nearly seven per cent in average CO2 emissions, Land Rover finished 31st in the table. However, the 4×4 manufacturer will release the its cleanest model ever in the shape of the Range Rover Evoque next year, meaning a much improved performance is expected next time.