Where did you get the information about the tax going up? the only stuff I can find is showing this years rates on the DVLA website that says the higher rate applies only to vehicles registered after 23/03/06
The cost of vehicle tax for cars, motorcycles, light goods vehicles and trade licences : Directgov - Motoring
And I really can't see how having to pay twice the tax will stop people using there cars...the tax if not related to how much you use the car, its an ownership tax, so if I have to pay twice as much then why should I leave the car at home and find alternative means of transport...it makes no sense to raise taxes on cars in this way that already exist.