“The government has given financial assistance to Birmingham, Bristol and Portsmouth to help fund their clean air zones but has refused to support London’s scheme, arguing that powers over transport and air quality are devolved to the capital.”
The problem with No. 10 is that there's no one in there old enough to remember walking to school through winter smog. Pollution kills and legislation saves lives: https://en.wikipedia.org/wiki/Clean_Air_Act_1956