Drivers of gas-guzzling cars will have to pay £25 to enter London's Congestion Charge zone under plans announced today.

As part of his crackdown to tackle climate change, the London mayor Ken Livingstone is proposing to introduce an emissions-based charge that to hit drivers of high-polluting vehicles.

It means that drivers of some 4x4s and vehicles with CO2 emission above 225g per km, pay the top charge.

This new levy could be imposed by 2009 or 2010, but Mr Livingstone confirmed he has asked Transport for London, to see if this could begin earlier. Vehicles the produce less than 120g CO2 per km will pay nothing.

The current £8 charge will be levied upon vehicles with CO2 emissions between 120g and 225g per km. The 90% resident's discount for those living within the C-Charge zone will be withdrawn for the heaviest polluting vehicles.

Motoring organisations have praised the plans to remove fees for low-polluting cars but are concerned about how the top-rate charge will affect owners and manufacturers.