//...if you must drive a polluting vehicle into their city and contribute to the pollution problem then it is not unreasonable for that to be taxed//
I would suggest that it is unreasonable because vehicle owners already pay enormous sums in tax whilst the owners of the most polluting pay more than most courtesy of the RFL being based on emissions. But leaving that side I have two issues:
1. If these vehicles are so hazardous why doesn't the Mayor simply ban them?
2. Huge swathes of the "London" that this charge effects are in fact open countryside. Here's a couple of examples:
This is where the London Borough of Bromley begins:
https://www.instantstreetview.com/@51.36706,0.147247,321.54h,5p,1z,3G94tqOhSAbK9xV1LPye4Q
And this is where the London Borough of Havering ends:
https://www.instantstreetview.com/@51.541914,0.333437,90h,-4.18p,1.56z,9zf6qMT1W-fUU5eD6M83_g
Wander around using Streetview and you will see these are not built up areas - in fact you will struggle to see a building at all and few vehicles are visible from the Google camera car. These are not isolated examples. The exurbs of the outer London boroughs - especially Bromley, Havering and Hillingdon, consist of huge areas like this. The view of the Bromley boundary I have provided is actually in the centre of a large area of farmland and woods which stretches between the eastern edge of Orpington and the M25. The M25, of course, is not included in the ULEZ zone (even though it passes through the easternmost part of the London Borough of Havering, with part of that borough being outside the orbital motorway). It is ludicrous that the few vehicles using an assortment of country lanes running through farmland are subject to a pollution charge whilst tens of thousands of vehicles ploughing along an adjacent motorway are not.
Many people do not realise that large parts of the outer London boroughs are like this - they are not all like Park Lane and Piccadilly.