I don't see what's wrong with the idea of pay-per-mile for everybody, and scrap road tax for everybody.
I've never seen anybody say that the basic idea of paying for goods and services on the basis of the more you use the more you pay is wrong. We have pay-per-pint for beer. Pay-per-litre for petrol/diesel. Pay-per-kWh for electricity. Pay-per-kg for potatoes. Why not pay-per-mile for road use?
Right now if Bill has two cars and does 5,000 miles per year in each, and Ted has 1 car and does 20,000 miles per year in it, Bill pays 2x what Ted does rather than 50%.
Is that fair?
Imagine if we'd had p-p-m for the last 100 years, and the govt said we're going to abolish that and replace it with a per-vehicle annual charge. Imagine the howls of outrage about the unfairness of that from people who had more than one car.