Cars are getting cleaner, according to CO2 emission level figures out today.

Average new car C02 emissions fell 4.2% in 2011 and have reduced by 23% since 2000, the Society of Motor Manufacturers and Traders (SMMT) said.

But the average new-car figure of 138g of CO2 per one kilometre (138g/km) was higher than the 2015 European legislative target of 130g/km.

SMMT figures showed that in 2011, a total of 46% of new cars had emissions below the 130g/km figure. Also, more than 65,000 vehicles were exempt from having to pay vehicle excise duty as they were below 100g/km.

Executive cars (down 9.5%) and specialist sports cars (down 7.0%) showed the biggest fall in emission levels last year compared with 2010, while executive cars (down 34.9%) and cars in the Mini sector (down 29.9%) made the biggest emissions improvements since 2000.

The Mini sector had the lowest average emission levels among new vehicles last year - at 107.8g/km - while luxury saloons had the highest at 221.8g/km.

New cars in 2011 were 18% cleaner than the UK average.

Diesel cars took a 50.6% share of the market last year, while alternatively fuelled vehicles had a 1.3% share.

SMMT chief executive Paul Everitt said: "The UK motor industry can be proud of the progress it has made in reducing CO2 emissions and improving fuel efficiency.

"The industry recognises its responsibilities and the industrial opportunities from the transition to ultra-low carbon vehicles. Future environmental and economic success will be determined by sustained investment in new technology, research and development, infrastructure and consumer incentives.

"We are seeing steady improvement in conventional technologies and the emergence of a range of alternative technologies, creating one of the most innovative periods for the global automotive industry."