Perhaps there should be different road tax levels based on higher power.
This is already the case in japan car tax for cars of 660cc is only £25
above it its quite a lot more i think but i dont remember.
maybe go up in 0.4 steps. so at 1 litre £50 1.4-1.8 £100 1.8-2.2 £200 2.2+ £400 etc
You see how i nicely put my car of 1.2 in the cheapest bracket hahaha