Average carbon dioxide emissions from new cars in the UK are falling, official figures showed.

But progress towards "greener" cars is far too slow, environmental groups said.

New cars in 2005 emitted 169.4 grammes of carbon dioxide (CO2) per kilometre (expressed as g/km), the Society of Motor Manufacturers and Traders (SMMT) said. This figure was 1.2 per cent down on the 2004 figure and 10.7 per cent down on the figure for 1997, the SMMT added.

It also announced that 18 per cent of new cars now have CO2 emission levels below 140 g/km which is the target figure for all cars by 2008. In addition, half the new car market is now under 160 g/km.

SMMT chief executive Christopher Macgowan said: "Our latest data shows the progress we are making to bring ever cleaner vehicles to the market place.

"We need an integrated approach if we are to keep making good progress. In addition to our technological advances, buyers need incentives to encourage them into cleaner vehicles."

Warwickshire had the highest CO2 emissions in 2005 at 190.6 g/km. West Glamorgan, at 162.1 g/km, had the lowest.

Jason Torrance, campaigns director for environmental group Transport 2000, said: "This is a disappointment. The UK car industry is set to miss its target to reduce emissions by 2008 by a wide margin.

"In effect, they've set themselves the task of driving from London to Edinburgh, but have been dawdling and are only likely to get as far as Scotch Corner in North Yorkshire, if that."

Friends of the Earth's transport campaigner, Tony Bosworth, said: "The UK motor industry is failing to take its environmental responsibilities seriously. It will almost certainly fall way short of the European car manufacturers voluntary target for cutting pollution from new cars. This is why mandatory targets for greener cars are needed.

"Road transport is one of the biggest contributors to UK CO2 emissions. The UK Government must do more to encourage people to buy greener vehicles, and take steps to cut traffic on our roads as part of a determined effort to tackle climate change."