CO2 emissions from new cars 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.

“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,” said SMMT chief executive Paul Everitt.