Motorists with an environmental conscious have been warned to check that their car is really as ‘green’ as it seems after a new study revealed that some vehicles are polluting more heavily than they did five years ago.

The research, carried out by the International Automobile Federation (FIA) Foundation’s EcoTest, involved testing a range of 14 models in urban conditions for factors like carbon dioxide emissions, and other pollutants including hydrocarbons, carbon monoxide and nitrogen oxide. It found that many models which improved their environmental performance still fell well short of the minimum levels now possible and renowned green car manufacturers including Honda, Renault and Daihatsu were among the worst offenders.

The Renault Scenic for example, which has been touted as ‘the UK’s greenest car’ saw its ‘greenness’ rating fall by five points to 61 out of 100. The Daihatsu Cuore, sold in Britain as the Charade until 2006, slipped from 61 to 57.

Honda claims to be an environmental leader with green credentials seen in every product – yet the Accord Tourer’s score fell from 71 to 68.

However, Honda did have the consolation of the biggest improvement among the models tested – the Honda FR-V leapt from 47 points to 65; while the VW Touran enjoyed a 14 points increase up to 62.

Mazda meanwhile had a mixed bag in the test results – with both the best and worst performing cars. The Mazda6 secured the highest overall score at 80, while the Mazda2 was the worst performer with just 52.

According to David Ward, the foundation’s director-general, consumers must be careful to seek independent information about green cars.

He said: “The results of our survey are a warning to motorists that all is not what it seems when it comes to buying greener cars.

“The motor industry has a long way to go in order to achieve the lowest levels of CO2 emissions, pollutants and optimum fuel economy.”