ANALYSIS: Alistair Darling the cash guzzler

Alistair Darling's much-trumpeted 'green levy' on motorists announced in his first Budget would double car tax revenue to £4.4billion  -  but reduce vehicle emissions by only a fraction of 1 per cent.

The main result of the hikes, therefore, is that owners of popular family cars, estates and people carriers will pay hundreds of pounds more for the privilege.

And they will be penalised even if they bought their run-around up to eight years earlier.

From April, there will be 13 bands for car tax ranging from £440 to zero depending on greenhouse gas emissions, replacing the existing seven groupings.

Some vehicles with higher CO2 outputs will jump several bands.

More significantly, the present system where high-polluting cars are exempt from the top rate if they were bought between 2001 and 2006 will be swept away  -  meaning road tax will double for some of Britain's biggest-selling models by 2010.

So, when motorists bought their cars a few years back  -  well before 'green' taxes were top of the political agenda  -  they most probably did so based on the size of their family and the essential journeys they made, rather than the vehicle's environmentally-friendly credentials.

Some of the biggest rises are planned for drivers of mid-range family cars.

However, the tax rises for Porsches and Rolls-Royces will be less  -  fuelling claims that poorer and middle-income families are once again bearing the brunt of Labour's tax regime.

One glaring example is that the cost of a tax disc for a Nissan Micra will rocket by eight times the rate of inflation to 24 per cent while the bill for a gas-guzzling Hummer rises by only 14 per cent.

Official Treasury projections show that the amount of revenue raised from vehicle excise duty will increase from £1.9billion in 2007 to £2.9billion this year, £3.7billion in 2009 and £3.9billion in 2010.

From then, there will also be a higher first-year rate  -  the showroom tax  -  for new cars to discourage buyers from choosing higher polluting vehicles, netting a further 520million.

This will be levied on all cars emitting more than 130g of CO2 per kilometre when they are bought and varies from £115 to £950.

Few hard-pressed families already struggling with higher food and household bills will be able to afford a new eco-friendly car  -  and anyway, the changes mean the re-sale value of their existing motor will be greatly reduced.

Experts also point out that once the road tax is paid, drivers can then use their cars as often as they wish without being penalised for polluting the air.

'It is a weakness that the argument put forward for this is that it is an incentive to buy less gas-guzzling cars,' said John Cullinane of the Chartered Institute of Taxation.

'It is making a nonsense of spending decisions one made in the past. You are being penalised for buying a gas-guzzler years ago.'