New congestion charging rules have come into force in London as part of plans to halt the increasing number of diesel cars in the city.

As of July 1 this year, only cars that emit less than 75g/km of carbon dioxide will qualify for congestion charge exemption. The move rules out all traditional internal combustion-engined cars and leaves plug-in hybrids and full-electric cars as the only vehicles to escape the charge.

Previously Transport for London had allowed cars emitting less than 100g/km to enter the city centre free, but the vast majority of qualifying cars were diesels, which still for the most part emit significant quantities of harmful nitrous oxide, or NOx. As such the Mayor, Boris Johnson, has taken the only step within his power to dissuade diesel cars from entering the heart of the city.

The change was initially announced several months ago, at which time the Mayor effectively gave around three months’ ‘grace period’ to those about to buy a car rated at sub-100g/km. Those vehicles bought before the end of June will still qualify for congestion charge exemption for three years, whereas an identical car bought on or after July 1 will not.

Makers of electric cars, like Renault and Nissan, have seized the opportunity to promote their own environmentally friendly transport, with more effort than ever being put into advertising plug-in cars like the Leaf and Zoe.

The lowest-CO2 internal combustion cars currently include several models from different manufacturers that are hovering in the mid-80s grams per kilometre. These cars are all diesels, so in time the problem of ‘dieselification’ in London is likely to repeat itself.