It saves money and nobbles the tax dodgers.
Roads tax can be evaded and isn't paid by foriegn trucks and cars. Therefore do away with it and put it on petrol. Then it can't be dodged and the user pays pro rata for his use of the highway.
There would need to be isurance disks and MOT discs for car windscreens.
We could SAVE MONEY and do away with a complete government depart ment.
Foriegn truckers would compete on an equal basis with our own if they had to pay tax on any fuel they imported.