A senior Tory MP has urged Chancellor Alistair Darling not to give motorists "an easier ride" over green fuel taxes.
Giving in to demands for lower duty would be catastrophic for the fight against climate change, Tim Yeo, chairman of the Commons Environmental Audit Committee, warned.
He also insisted that highly controversial moves to tax owners of the most polluting vehicles even more highly were right "in principle".
Ministers are said to be putting Mr Darling under pressure to scrap a 2p hike in fuel duty planned for the autumn as record-high oil prices increase the burden at the pumps, but Mr Yeo said fuel duty had actually fallen in real terms since 1997 while carbon emissions from transport had risen by 12%.
"The Government's actually been weakening its tax measures to deal with carbon emissions, and it would therefore be a grave mistake if they were to reverse those now," he said.
"To try and say now we are going to let people have an easier ride in terms of green taxation on fuel would be catastrophic in terms of our response to climate change."
His comments come as more than 1,000 hauliers descended on London in protest over fuel taxes.
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