Some 9.4 million motorists will have to pay more road tax in the crackdown on carbon emissions, the government has admitted.
Vehicle excise duty will rise for 43 per cent of vehicles made since 2001 by up to £245 for the most polluting ones, according to official estimates.
The Conservatives said the prime minister had misled parliament on the issue.
Shadow chancellor George Osborne said: "This destroys the government's defence that this is a green tax and in general gives green taxes a bad name."
Liberal Democrat transport spokesman, Norman Baker, said the government "must have a death wish" by introducing taxes which penalised people for having cars chosen several years ago.
Environmental groups urged the government to stand firm and raise excise duty to invest in better public transport.
The estimates were revealed in a parliamentary answer by Treasury minister Angela Eagle when giving evidence to the Environmental Audit Committee.
Ms Eagle said in 2009-10 a third of cars will be better off in real terms, with 55 per cent of cars "no worse off".
More than 44 per cent or 8.7 million vehicles, all in the six top-polluting bands, will pay more, she said.
But for 2010-11, 18 per cent or 3.9 million people will pay less tax, while 39 per cent or 8.5 million will see no difference.
The Treasury is set to receive more than £1 billion in additional revenue from the scheme by 2011.
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