An easy way round this, you pay your "tax bill" for your car when you have it MOT for the miles done that year, also add to this that you must MOT a car before its sold so that unroad worthy cars are not being sold on, and every car would then be sold with 12months MOT on it.
Ive just had my bike tax come through as its a 650 (falls into the over 600 bracket) its gonna cost me nearly 80quid for the year, in the last year I only did 750miles on the bike gets very expensive for a fairly economical vehicle.