The findings come ahead of the publication of JATO's latest report – A Review of New Car CO2 Emissions across Europe 2013 – which covers 23 European markets, and shows that 15 of the top 20 brands achieved average emissions below 130g/km.

JATO’s data shows that all 23 markets recorded reduced average CO2 emissions from new cars in 2013 compared to 2012.

The Netherlands recorded the lowest average emissions at 109.0g/km, and was also the most improved market. The 9.7g/km drop from 2012 was driven by a tax regime that encouraged the purchase of the lowest-CO2 cars.

Greece maintained the second place it gained in 2012 with 111.3g/km, and was also the second most improved market as diesel cars took a 57% share of this long-time petrol-dominated market.

Portugal slipped from first to third place, with a still impressive 111.6g/km average. Denmark and France recorded average emissions below 120g/km, making France the first Big 5 market to break the 120g/km barrier. Italy recorded 120.7g/km, while Spain and Great Britain recorded averages between 120 and 130g/km. Germany's average emissions of 135.9g/km, a 5.2g/km improvement over 2012, marked the first time its average has fallen below 140g/km.

Of the markets studied, only Switzerland recorded average CO2 emissions over 140g/km, but its 144.7g/km recorded in 2013 is a significant improvement over the 151.3g/km recorded in 2012.

Gareth Hession, vice president for research at JATO Dynamics, said: ‘While all countries recorded a reduction in average CO2 emissions, the gap between the lowest and highest emission countries is widening due to differences in economic conditions and government initiatives.’

Amongst the volume carmakers, Renault recorded average CO2 emissions of 110.1g/km in 2013, an 11.2g/km improvement over 2012 (the greatest improvement of all the volume brands). While the brand's total of over 9,000 electric cars registered in 2013 contributed to this performance, the greatest improvement came from other product actions. The new Clio and Captur together accounted for over 45% of the brand's total volume, and averaged 103.9 and 105.6g/km respectively, while powertrain improvements improved the average emissions of most of the rest of the brand's models.

Peugeot maintained second place with 114.9g/km. Again this was the result of two key new small products, the 208 and 2008, commanding a greater share of the brand's sales, along with incremental improvements across the model range.

Toyota took third place with 115.9g/km, with improved emissions from the latest Auris and RAV4 models backed up by increased sales of hybrid versions of the Auris and Yaris, while Citroën claimed 4th place with 116.2g/km, driven mostly the introduction of new 3-cylinder petrol engines to the C3 model.

After six years of holding the title of the volume brand with the lowest average CO2 emissions in Europe, Fiat posted reduced average emissions of 118.1g/km. The brand's most efficient cars, the Panda and 500, remained mostly unchanged for the year, while the 500L MPV, now including a larger seven-seat version, significantly increased its share of the brand's sales.

Gareth Hession concluded: ‘Manufacturers are putting great effort into ensuring each new model is more efficient than its predecessors, with results that benefit consumers including lower running costs and reduced environmental impact.’