I recently wrote to the ULEZ office to ask why Classic Minis were charged. Their response will likely be that the Mini wasn't Euro 4 compliant. How could it be? The Mini didn't live to see Euro 4 standards implemented.
Upon further review, EURO 4 has the following requirements for Petrol vehicles:
CO - 1.0 g/km
THC- 0.1 g/km
NOx - 0.08 g/km
When you compare this to the emissions data published, it would appear that injection Minis (at minimum) meet these:
Wanted to check in with other Mini owners if there is appetite to challenge the TFL on this and seek an exemption for the classic Mini?