Lets say you had a 1999 petrol car with emissions that would meet EUR4.
EUR4 hadnt been invented so in 1999 you'd be awarded EUR2

The London ULEZ requires EUR4 and because this standard was introduced after this vehicle was marketed in the UK you will thereforehave to pay a daily road use fine

Surely it is the emissions not the legislation in force at the time of manufacture that should determine eligibility?

What is being done to challenge this bureaucratic blindness or ideological indifference to the reality of the issue? There must be plenty of cars that can meet higher standards (of lower emissions) than those mandatory at the time in any particular market