Current owners of vehicles that are exempt from the charge (those emitting less than 100g/km) will still be eligible for the full discount for a further three years in what Johnson described as a "sunset period", ending 24 June 2016.

The move means that at present, only plug-in hybrid and fully electric vehicles will avoid the charge when the new rules come into play.

There are no existing petrol, diesel or conventional hybrid vehicles on sale with low enough emissions to qualify for the discount.

Further regulation changes include an £10 increase in the penalty charge on 20 May from £120 to £130 for those who fail to pay and the removal of the ability to pay for the charge in shops from 26 July, which according to Transport for London accounts for only 6% of existing payments.