A plan to make people in smaller vehicles exempt from the London congestion charge could actually produce more carbon emissions, it has been claimed.
Clean Green Cars instead believes that automobiles putting out 110g per km and below should pay a nominal charge of £4.
The group believes that by allowing people in for free, more motorists will buy smaller cars and increase the amount of harmful gas outputted.
It added that it makes sense to charge all cars that enter the zone as London Mayor Ken Livingstone has stressed it is a congestion cost that is being paid – not a carbon emissions tax.
"[Clean Green Cars] believes that reworking Transport for Londons proposed framework for an emission-based charge could have a more positive impact," said the firm.
Meanwhile, Greenpeace has revealed that agriculture is responsible for up to 17 to 32 per cent of greenhouse gas emissions.