I guess this is a topic in which a large number of motorists will have an interest - if not today, then tomorrow!
With "Low Emission" zones proliferating like the proverbial rabbits, there cannot be many who will never run foul of some restriction or other - even when well signed, it can be well-nigh impossible to scan all the street furniture, identify all the signs, then read and understand them, whilst simultaneously taking care to avoid rear-ending the vehicle in front.
So Martin, having been picked out for driving his (not commercial) van in an area where only private cars are permitted free passage, has decided to contest the claimed infraction on the basis that his van is a private conveyance in all significant respects and is therefore permitted free passage.
Of course, as he digs deeper he uncovers more issues ... which seem as if they may have parallels with the Council Tax situation. Quelle surprise!