The average new car is 12.6% more efficient than its predecessor, according to the SMMT. Yet in September 2018, average CO2 emissions of the new cars registered in the UK reached a six-year high of 128.3g/km.

The rise in CO2 emissions is the latest by-product of the Dieselgate scandal, and the biggest jump yet in an upward trend since CO2 emissions reached a low of 119.2g/km in August 2016. 

Electrified cars are not selling at the same rate as the diesel decline, so buyers are returning to petrol, and CO2 emissions are going up. CO2 emissions will increase further in the short term with the more real-world-representative WLTP economy tests.