I think the pedantic argument about 'Road Tax' has run its course, what? Shall we agree that when someone bleats about 'paying road tax' we all concede that he or she's referring to that little circle of paper and move on, yes?
What is more bothersome is your MC'ist's utterance (expletive deleted):
"Biker: I pay Road Tax and I can do what I want!!!"
You could try explaining to him, that 99.9% of all road users (including a large majority of cyclists and pedestrians) are also coughing up annually for that paper circle. So if each and every one of them can 'do what they want', then where are we???
Like the near-miss I witnessed this morning, between a pick-up truck and a car, on a roundabout (I was well out of the way

) I didn't catch the words in the following altercation, the car driver was in the right seeing as he was already on the roundabout, the pickup driver entering the R/B just 'did what he wanted' presumably because he 'pays road tax'...
The only person who really could 'do what he wanted' on the roads was the late dictator of a certain African country, who decreed that the centre lane in every road was reserved for his limo and no other vehicle...