I think the story changes because nobody really knows what the detail of the truth actually is. Also it is reported by the media; the media, as you well know, (a) don't understand things and (b) change the emphasis on things to produce a story that will sell papers or what have you.

The fact that governments use the change of governing party as way of justifying raising taxes has absolutely nothing to do with global warming. That is simply just a red herring.

As far as I'm concerned the tax on all but the most efficient vehicles should be raised by a very high amount. And the money raised should be put towards incentives for people to get energy efficient things (heating, transport, etc.), proper insulation, public transport infrastructure, reducing waste (including litter), etc.

People who can justify their need for things like SUVs (see my second comment to didiusjulianus) should be able to claim for a tax refund, or something similar. However, I can see this as potentially being open to abuse.