heres a thought, but if i had the powers to make it so, i would rethink the car tax theory this way:
tax is calculated at MOT time based on your nasty particles emission, thus more people are encouraged to better maintain their vehicles, use less polluting fuels, and best of all, everyone could have a V8! (on lpg - or possibly landfill gas..or even cowfarts)
would also mmake a few changes in the immigration department aswell.. (dont wish to offend anyone tho)
perhaps a collabortation of ideas could be sent to 10 downing street?? :D