Almost nine million car owners will lose out under the controversial changes to vehicle excise duty (VED), it has emerged
Exchequer Secretary Angela Eagle disclosed the Government expects 44% of cars to be hit under the new rules, which sees higher taxes for the most polluting vehicles.
Official figures predict that 8.7 million vehicles will see tax increased in 2009-10 - all in the six most-polluting bands.
Ms Eagle gave the figures in a Commons written answer to shadow Treasury minister Justine Greening.
Ms Eagle said: "As a result of the Vehicle Excise Duty reforms announced at Budget 2008, in 2009-10, it is estimated that within the 13 new bands, a third of cars will be better off in real terms, and in total, approximately 55% of cars will be no worse off."
The controversial changes to VED were unveiled by Chancellor Alastair Darling in his first Budget speech earlier this year, doubling the tax on some family saloons to £455.
They attracted criticism from all sides, with 50 Labour rebels signing a Commons motion branding the changes "retrospective" because they will apply to all cars registered since March 2001.
Earlier this month the Government staved off Tory amendments to the Finance Bill which would have seen the plans scrapped.
The AA said Ms Eagle's admission "confirms our worst fears" while Shadow Chancellor George Osborne accused Prime Minister Gordon Brown of seeming to mislead Parliament over the figures.
Mr Osborne said: "Gordon Brown appears to have misled Parliament. He said that the majority of drivers would benefit from the changes to VED.
"Now even the Treasury have admitted that just a third of drivers will be better off in 2009, dropping to less than 20% in 2010. This destroys the Government's defence that this is a green tax and in general gives green taxes a bad name.
"We need the Prime Minister to tell us whether he knew that he was giving Parliament the wrong information and was treating the public like fools, or was it the case that he didn't know the truth about the impact of his own Budget on families?"
AA President Edmund King said: "This admission confirms our worst fears. The figures show that at least nine million motorists will be hit in the wallet next year and the following year.
"Politically this could be dangerous particularly if an election is on the cards. The Treasury has made a mistake and must now scrap the 'retrospective' nature of the tax disc changes for older vehicles.
"This is not a green tax but a mean tax that will hit millions of hard-up families. Coupled with the record pump prices this will bring double misery to millions of motorists."
In a separate answer, Ms Eagle said five of the UK's 30 most popular cars would pay more under the changes. These were the 2.2l diesel Land Rover Freelander, the 1.6l unleaded Toyota Auris, the 2.2l diesel Honda CR-V, the 1.8l unleaded Vauxhall Vectra and the 1.6l unleaded Vauxhall Zafira.
Treasury officials claimed "nothing new" had been revealed by the figures. A spokesman said: "As we have consistently made clear, under the new bands of VED, the majority of motorists will be better or no worse off and for 25 of the 30 most popular models of cars, drivers will be better or no worse off."