You can point to the Ultra-Low Emission Zone (ULEZ), which means you can't drive in to very central London (where most people work, but almost noone actually lives there) with a petrol car or van that is older than 13 years. Doesn't sound ultra low to me, compared to hybrids have been produced for more than a decade and electric cars are available to the mainstream. And even this very low bar is enforced to the very inner boroughs only. The 50 years old diesel trains that are running its per-carriage engines at the platform when idle, are an exception of course.
I meant it has been happening since the EU-wide regulation came out. London reaches the critical yearly level at the first weeks of January and only cosmetic changes have been applied. E.g. a 20-year-old, rusty diesel truck, that makes ~£500/day gets away with £12.5 fee instead of ban from Greater London. The actual polluters won't invest in newer vehicles, because the lease is more expensive than just £12.5 per day.