More than half of Britain's 26.6 million drivers will receive higher bills with owners of many popular family saloons seeing their bills double.
The latest figures apparently contradict assurances given by Gordon Brown, Alistair Darling and other ministers that the majority of drivers will be "better off or no worse off" following the controversial changes to reform vehicle excise duty (VED).
The statistics were slipped out by the Treasury in answers to Parliamentary questions as MPs left for their 11-week summer break sparking allegations that the Government was trying to hide bad news.
The Conservatives accused ministers of misleading the public over the impact of the proposed changes.
Justine Greening, the shadow Treasury minister, said: "The Treasury have now been exposed for deliberately covering up the truth of their road tax hike - that the majority of motorists will be hit paying more road tax next year.
"These rises are retrospective for many drivers and will have virtually no impact on emissions. Gordon Brown is clobbering hard pressed families for more road tax when they can least afford it. When will Mr Brown ever give families a break?"
The figures reveal that 5.687 million people who own cars bought before 2001 will see their road tax increase by £15 to £200. The rise applies to anyone with an older vehicle with an engine above 1,550 cc.
For cars bought after 2001, the current system of seven levels of VED will be replaced with a new system of thirteen different bands. The bands are based on a vehicle's carbon dioxide emissions.
More than 7.93 million owners of newer cars will also pay more. The biggest increases will be for people who bought cars between 2001 and 2006 who could see their tax increase from £210 or less to more than £400 by 2010.
The figures reveal that 3.964 million people will pay the same road tax next year and just over nine million drivers with greener vehicles will receive reduced bills.
The Prime Minister and Chancellor are now under intense pressure from Labour MPs to water down the proposed changes.
The Telegraph has also been campaigning for the Government to abandon the plans.
More than 50 Labour MPs are threatening to vote against the plans and Mr Brown, who was damaged by the row over the abolition of the 10p income tax band, is understood to have privately indicated that he is prepared to back down on some of the changes.
Mr Brown is thought to believe that although the general thrust of the tax changes to reward greener cars is correct some of the detail of the proposals could be renegotiated. The Government has already agreed to postpone a two pence rise in fuel duty which was due to be introduced in the autumn.
Matthew Elliott, Chief Executive of the TaxPayers' Alliance, said: "From the outset this has been a cynical tax grab that is more greedy than green. The proposals are another body blow for families already struggling under the weight of high fuel prices and record tax bills."
The AA is now calling on the Government to be more open about the impact of the proposed changes and for the Treasury to publish full details of which vehicles will pay more on its website.
Edmund King, the President of the AA, said last night: "We have said to the Treasury at the very highest levels that there is so much confusion and mis-information about these changes that they should just publish all the information in plain English. It is still incredibly difficult to work out the implications and we need much greater transparency."
The Treasury insists that it has not misled the public and that cars bought before 2001 are not included in the reform package which ministers are referring to when claiming most motorists are not worse off.
A spokesman said: "As we have made clear, pre-2001 cars are not included in the reforms. We set out the position very clearly in the Budget, and have repeatedly said that under the new VED bands a majority of motorists will either pay less or the same in real terms.
"Rates for pre-2001 cars will continue to be based on engine size."
