Carbon dioxide emissions from new cars in Britain fell by their biggest ever margin in 2008 with the average model now emitting just 158.0g/km - 4.2% less than the 2007 figure and 16.8% down on the 189.8g/km base level in 1997.

The figures, revealed in the Society of Motor Manufacturers and Traders' (SMMT) annual New Car CO2 Report, showed that while the number of cars on the road and the distance travelled has increased, their share of total UK emissions continues to fall. Cars now account for just 11.5% of the country's total CO2 emissions, largely as a result of new technology, improved fuel consumption rates and better consumer awareness.

CO2 emissions have fallen across all market segments with the larger end of the market making some of the biggest improvements. In addition, increased consumer awareness and changes to vehicle taxation have resulted in a move towards 'best in class' choices with most consumers opting to buy a model with CO2 emissions within the bottom quarter of their preferred segment's range.

"The motor industry has made enormous progress in its work to cut the environmental impact of its products but more must be done if the tough targets set by European legislation are to be met," said SMMT chief executive Paul Everitt.

"Maintaining a steady rate of fleet renewal is vital to this success so the recent fall in new car registrations presents more than an economic challenge. Again, we urge government to implement a scrappage incentive scheme to take older, high-emitting cars off the road and boost the new car market."

The adoption of the new car CO2 regulation in December 2008 set a phase-in target for vehicle manufacturers to ensure their average fleet emissions do not exceed 130g/km by 2015. In the UK, there are already 236 models emitting less than 130g/km on the UK market but for the target to be met, an annual improvement of 2.5% per year must be maintained.