The tax is only a "planned" increase. I'm in the car trade and have studied this rigorously as it will severely influence what we buy and what's likely to sell towards the end of this year and start of next year. I personally have specifically bought an X plate car because of this.
Not too many people are aware of the planned changes yet and they could still change in the next budget. If they do change however it is most likely to target the pre-2001 cars (X reg and older) is an increase in the tax of the pre-2001 X plate or older cars. They can't tax these cars based on emissions as they don't have the required data, but a more likely increase would be to introduce a greater number of bands based on engine size (data that is available).
Either this change takes place or we will certainly see a situation where an X plate car is worth more than a Y plate car of similar age. If I had a Y plate I'd be worried. 02,52,03 cars will probably suffer a bit but will still be worth more because of the age difference.
As for the cost of it, if you believe in the environmental thing and global warming you have to believe it's for the best. If, like me I hasten to add, you think it might all just be part of the natural cycle of things and I'll be long dead before it really affects me anyway then you have cause to complain, but nobody is listening. It's really not cool to be anti-environmentalist, just ask Clarkson, and no government in the world can be seen to be such.
I asked my girlfriend this question the other day when she complained that the diesel for her car cost £1.16 per litre;
"How much would it have to be before you stopped buying it and got on the bus, or walked, or cycled, or car-shared?"
She couldn't answer it. The price could be £2 a litre and she'd still pay it, as would I, as would most of us and we'd complain in the pub and maybe vote the other way but nothing can break the scarcity value of oil. There is no real alternative.
The same applies to the car tax. Ask yourself "How much is too much?".