The daily charge is only for vehicles not meeting the ULEZ standards. For petrol vehicles this means meeting the Euro 4 criteria from 2005, for diesel it means

The daily charge is only for vehicles not meeting the ULEZ standards. For petrol vehicles this means meeting the Euro 4 criteria from 2005, for diesel it means meeting the Euro 6 criteria from 2014. It's hardly a surprise approximately 96% of vehicles are estimated to be ULEZ compliant in Greater London. I think this article is mixing up correlation vs. causation. Funny sidenote: since the ULEZ now covers Heathrow, what's the charge for an Airbus A380?