The UK is backing European Commission (EC) plans for introducing compulsory carbon dioxide targets for new cars.
Transport Secretary Ruth Kelly has launched a consultation process on the plans, in which the EC wants to introduce an average limit of 130g/km of carbon dioxide across car manufacturers' fleets by 2012.
The Government says the limit will help tackle climate change and encourage the development of technology that will improve the fuel efficiency of new cars.
However, the Government also wants the EC to go further and adopt a target of 100g/km of CO2 by 2020.
This, says the Government, would deliver a cut in CO2 emissions from new cars by an extra five million tonnes a year by 2020, in addition to the six million tonnes that would be cut under EC proposals.
It could also reduce the running costs of new cars by about 500 a year by 2020, a particularly important consideration at a time of rising oil prices.
The Government has also welcomed provisions in the EC proposals for setting different targets for manufacturers producing small numbers of cars, many of which are based in Britain.
Kelly said: 'Tackling climate change is one of the single most important issues we face. Harmful road transport emissions continue to rise and it is important we act now to reduce them.
The consultation runs until October 3.