Politics environment: Tories say 2.3m motorists to lose out in backdated green car tax. The Guardian

Tories claim more than 2 million worse off by government plans to up tax on environmentally unfriendly vehicles

In an attempt to force a rethink, the Conservatives warned that the changes would hit twice the number of people that have been left worse off by the abolition of the 10p starting rate of tax.

The Tories will today table an amendment to the finance bill that would prevent the rise in car tax, due to be introduced in April, from being applied retrospectively to vehicles bought since 2001.

The government, which responded to growing anger among motorists in May by indicating it would defer a rise in fuel duty in September, is indicating it has no plans to withdraw the increase in vehicle excise duty.

The change is designed to encourage people to buy low-emission cars, but it has been criticised by the Tories for breaking one of the main rules of environmental taxation: that taxes should encourage good behaviour, rather than punish past decisions.

The Tories said the government should act now because 2.3 million people - more than double the 1.1m households which are still losing out from the abolition of the 10p tax rate - would pay between £100 and £245 extra.

Drivers of family band F cars would be hardest hit in two ways:

· A total of 1.2 million motorists in this category, driving the Citroen C8, the Renault Espace and the VW Passat, would see their £210 car tax rise to £430 or £455 in 2010.

· A further 1.1m motorists in this category, driving the Citroen Picasso, Ford Mondeo, Vauxhall Astra and Honda Accord, would see their car tax rise from £210 this year to £310 in 2010.

Justine Greening, the shadow treasury minister, said: "Labour's backdated [vehicle excise duty] rises will double the pain for families struggling to cope, hitting twice as many people for up to twice as much as the 10p tax fiasco. Labour backbenchers joined us in making Gordon Brown see sense to compensate the 10p tax rate losers.

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