Just watched David Cameron duffing up Gordon Brown on the subject of green taxes. He rightly points out that if a green tax cannot change behaviour, it’s just a tax. Not his own idea, but very true.

If I have a five year old car and he puts the road tax up, the only way I can change my behaviour is to swap it for a new one which costs me less in tax but uses an awful lot of energy to produce.

So the only way a tax could influence my carbon footprint would be if it persuaded me to use my car less. And isn’t the way to do that a national congestion charge linked to excise duty??????