I'm loving the irony. SNP and LibDems leap to the attack when Labour in Westminster proposes to introduce a retrospective tax on the owners of cars with high CO2 emissions.

Meanwhile SNP and LibDem coalition administration proposes parking permit taxes based on, er, owners of cars with high CO2 emissions, that will apply to all car owners, so this too is, ahem, a retrospective tax on motorists. Nice timing. Surely they could have at least waited with this one until after the byelection is over? You would have thought they would - but in fact they were so keen to get this out, that it seems they even forgot to circulate the report to the opposition.

Although Adopted Domain is of course broadly in favour of Carbon taxes I do agree that the retrospective application of these taxes is slightly unfair - and in the case of Labours road tax, probably beyond what people would consider as reasonable.

Another problem with retrospective taxes is that they encourage people to buy new cars, and that isn't good. In most cases I suspect the most environmentally friendly form of car ownership is to keep a small engined old car on the road for as long as possible - even if it's emissions are slightly higher than a brand new car of equivalent engine size. That's my excuse for my half share in a total jalopy at any rate. Retrospective taxes based on emissions might encourage people like me to think about getting a new car though, despite all the extra energy and resources used to make it.

Provided they're implemented fairly then, I'm all in favour of big tax sticks and big tax carrots to encourage people into lower emissions cars, or in Edinburgh's case - the City Car Club. Afterall a ton of CO2 saved now is much more efffective and cheaper than having to save several tons later on.

The hysterical pro-motoring lobby are pulling out all the stops as usual, though, with an impressive call to 'think about disabled people' - who apparently need vehicles with large engines because they need to fit their wheel chairs in.

Surely the most ridiculous claim the petrol heads have made yet?