Government stands firm on road tax

In the Commons, Gordon Brown brushed off Tory accusations he misled Parliament when he claimed last month that the majority of drivers would benefit from the changes, which will see the tax on some cars rise to £445.

Meanwhile Labour backbenchers - who have been pressing ministers to abandon plans to apply the new rates to vehicles already on the road - warned they were ready to start "flexing our muscles".

The latest row follows the revelation on Wednesday by the Treasury that by 2010-11, 9.4 million drivers face higher bills - 43% of the predicted number of vehicles on the road.

Some 8.4 million will pay out around the same, while 1.4 million will see their payments fall under the changes, which are due to come into effect in April and are designed to hit the heaviest polluters the hardest.

Downing Street said the Government had no plans to reverse the changes, pointing to comments by Chancellor Alistair Darling in a recent newspaper interview. "He made clear that the policy remains the same," the Prime Minister's spokesman said. "The Government's policy was set out in the Budget."

However Labour backbencher Ronnie Campbell, who tabled a Commons motion signed by almost 50 Labour MPs calling for a rethink, insisted he had won assurance that Mr Darling would look again at the issue.

He signalled the rebels would not stand idly by if their demands were ignored. "I think we have got a commitment from Alistair to look at it in the Pre-Budget (Report) in October," he told BBC Radio 4's The World At One. "We're flexing our muscles and saying 'Come on, be careful here. You're going to tax these people, they're working class people, they're our core vote'. I think we should be thinking very carefully about this."

In the Commons, Tory leader David Cameron called on Mr Brown to apologise after he told MPs during exchanges in Prime Minister's Questions on June 4 that the majority of motorists would benefit from the changes. "Will he now correct himself and apologise to the House for getting it wrong?" he demanded.

Initially Mr Brown ignored the question, but when he was pressed again by another Tory MP, he said that Mr Cameron had accepted in his reply at the time that the majority would either be better off or no worse off - which is the Government's position.