Cars with CO2 emissions between 120-225g/km will continue to pay £8 per day.
The measures would add up to £6,500 in annual cost per demonstrator to dealers retailing specialist marques such as Porsche, Bentley and Ferrari within the Congestion Zone. Those carmaker's ranges currently all exceed the 225g/km ceiling.
The change is part of a package of measures that Livingstone may introduce to cut London's carbon emissions by 60% within 17 years. The capital is one of 40 cities worldwide which are pooling their knowledge to play a leading part in fighting climate change.