The "green levy" on motorists announced in Alistair Darling's first Budget will double car tax revenue to £4 billion but reduce vehicle emissions by less than one per cent, Treasury figures have showed.

The Chancellor announced a significant increase in car tax in March.

This will result in the owners of family cars, estates and people carriers paying hundreds of pounds a year more to use the roads.

Mr Darling claimed that the duty increase was designed to encourage motorists to switch to greener cars and to reduce the environmental impact of driving.

However, the Telegraph has seen Treasury projections which disclose that while the amount raised from car tax will more than double - from £1.9 billion to £4.4 billion by 2010 - carbon dioxide emissions from motoring are expected to drop by less than one per cent.

Justine Greening, a shadow Treasury minister who obtained the figures, said last night: "This is a massive tax hike which will have virtually no impact on the environment.

"Despite their claims, the Government don't expect this move to change behaviour at all - it is just another eco-stealth tax of the worst kind."

Some of the biggest tax increases are planned for drivers of mid-range family cars, including some models of the Ford Focus, the Renault Espace and even Nissan Micras.

However, the tax rises for Porsches and Rolls-Royces will be less - leading to allegations that poorer people are again being selected by a Labour tax measure.

The Conservatives have predicted that Gordon Brown will face a revolt similar to the 10p tax protest when ordinary motorists encounter the large duty increases next year and complain to their MPs.

The Budget announced a radical overhaul of the taxation system for cars - known as vehicle excise duty - claiming that the "majority of motorists will be better or no worse off in 2009".

However, that claim has been undermined by analysis showing that nine out of 10 vehicle models will be taxed more heavily from next year.

Under the scheme, cars will be divided into 13 groups for road tax purposes depending on their CO2 emissions. Annual road tax will then be charged at up to £440 for cars such as Jaguars, Range Rovers and even some people carriers, emitting more than 255g of CO2 per kilometre.

Cars producing less than 100g will not be taxed.

At present, there are seven bands, with the least green vehicles paying a maximum of £400. Some family cars will move up several bands.

The tax on a Vauxhall Astra 2.0i 16v or Saab 9-3 MY2008 will more than double, from £210 to £430. The owner of a Ford Focus 1.6 Duratec will pay 59 per cent more (£170 to £270), and tax on a Citroen Xsara Picasso will rise by 48 per cent to £310.

From 2010, there will also be a higher first-year rate - described as a showroom tax - for new cars. This will be levied on all cars emitting more than 130g of CO2 when they are bought and varies from £115 to £950.

Models attracting the £950 charge include Volkswagen Touaregs, the Audi A6 and A8 and Volvo V70s. Those in the next band - paying £750 - include Vauxhall Vectras, Mercedes M and E class estates, and Mitsubishi Shoguns.

The latest figures show that, following the changes, the amount of revenue raised from vehicle excise duty will increase from £1,923 million in 2007 to £2,920 million this year. It will go to £3,720 million in 2009 and to £3,920 million in 2010.

An additional £520 million will come from the showroom tax in 2010, taking the Government's tax haul to more than £4 billion.

Edmund King, the president of the AA, said that motorists would be "shocked" when they had to pay the higher levels of vehicle duty for virtually no environmental benefit.

"The draconian nature of the measures are not yet understood by the public who face a double whammy after also being hit with higher petrol prices," said Mr King.

"If the projected results of the move would be to significantly reduce carbon dioxide emissions, the motoring public would be more likely to accept it. But it just benefits Treasury coffers not the environment."

There are almost 30 million cars registered and the number increases by about 500,000 annually. Therefore, only a small amount of the extra tax take is down to a rise in vehicle numbers. 

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