It is what drivers of gaz guzzlers across the capital were hoping would not come to pass, but Mayor Ken Livingstone has rubber stamped plans to impose a £25 a day congestion charge on drivers of the most polluting vehicles.

The proposals had been under consultation, but speaking at city hall on Tuesday, Mr Livingstone granted approval to higher charges on so-called Chelsea Tractors.' Under the new rules, SUVs, high powered sports cars and luxury vehicles as well as those emitting over 225g per km of CO2 will be charged £25 to enter the congestion zone, while vehicles in road tax bands A and B that emit less than 120g per km will become exempt from the charge. Cars in bands C, D, E and F will continue to be charged £8 per day.

Of those cars currently driven in the Congestion Charge zone, 17 per cent would be liable for the £25 charge, and just two per cent are Bands A and B which would qualify for the 100 per cent discount.

The Mayor claimed recent polls showed widespread support for the idea. The new rules will take effect from October 27 and be reviewed in 2010.

"Nobody needs to damage the environment by driving a gas guzzling Chelsea Tractor in central London," Livingstone told the press.

"The CO2 emissions from the most high powered 4x4s and sports cars can be up to four times as great of those of the least polluting cars. The CO2 charge will encourage people to switch to cleaner vehicles or public transport and ensure that those who choose to carry on driving the most polluting vehicles help pay for the environmental damage they cause."

The initiative is part of Mr Livingstone's climate change action plan which aims to reduce the capital's CO2 emissions to 60 per cent below 1990 levels by the year 2025.

Friends of the Earth Director, Tony Juniper, welcomed the initiative. He said: "Measures that get people to choose greener cars, as well as to drive less, are urgently needed. Charging gas-guzzling vehicles more to drive in central London is extremely welcome and supported by most Londoners."

There will be no change to the size of the central London Congestion Charge zone.