Attempts by European carmakers to deliver lower carbon emissions slowed to a crawl last year, according to figures from green transport lobby group Transport and Environment (T&E).

In 1998 the European Automobile Manufacturers Association (ACEA) signed up to a voluntary agreement with the European Commission to reduce car's average carbon emissions to 140g/km by 2008. However, new figures from T&E claim that last year new cars sold in Europe by ACEA's members emitted an average of 160g/km, a reduction of just 0.2 percent on the previous year and the smallest improvement since the agreement was signed.

T&E said the results mean ACEA "will now almost certainly miss the target " and also increase pressure on the European Parliament to go through with plans to impose legally-binding targets on car manufacturers.

The performance of Japanese and Korean manufacturers were no better with average emissions for new cars standing at 161g/km and 164g/km respectively. The overall figure for all carmakers selling into Europe in 2006 stands at 160g/km, a reduction of 0.7 opercent on 2005.

"In the first eight years of their voluntary commitment carmakers concentrated on bigger, heavier and more gas guzzling cars, and the results speak for themselves," said Aat Peterse, programme manager at T&E. " Clearly, the voluntary commitment wasn't worth the paper it was written on and regulation is needed now more than ever."

He urged the EU to stick to plans for a legally-binding target of 120g/km for 2012 and begin work on a series of long-term targets leading to vehicle emissions of 80g/km by 2020.

However, there have been fierce debates within the European Commission about the proposed binding targets with some arguing they will lead to increased car prices and job losses, some supporting the targets but claiming they should not be implemented until 2015, and others insisting they should be made stricter still.

Meanwhile, car manufacturers have pointed to the emergence of a raft of new green cars in recent months as evidence it can improve fuel efficiency without legal targets. The ACEA has also called for a change to the planned targets that would see heavier cars such as SUVs face weaker targets and argued that CO2-related taxes on cars would prove a more effective way of cutting emissions.

The European Parliament is due to environment committee vote on a so-called 'opinion' on the proposed car CO2 regulations this week in advance of a formal legal proposal from the European Commission in December.