David Miliband, the Environment Secretary, confirmed yesterday the authenticity of a leaked letter in which he proposed to the Chancellor a series of new environmental taxes. The most controversial was a system of higher fuel duties that would keep the price of petrol up even when cyclical falls in oil prices would usually lead to cheaper forecourt prices.

This was a more sophisticated approach that would “maintain pressure on the cost of motoring” without the Chancellor having to announce potentially unpopular rises in fuel duty, he said.

Vehicle excise duty should be raised substantially for gasguzzling vehicles with higher carbon emissions to encourage drivers to switch to fuel-efficient cars, as the Government has done with company cars, he suggested.

Road pricing, for which the Government is expected to include powers in the Queen’s Speech even though it is a longer-term policy, should be set high enough to reflect the full environmental impact of journeys and encourage motorists to switch to public transport, Mr Miliband said.

He proposed a rise of £5 per flight in air passenger duty, raising £400 million that could be used to offset the carbon emission from aviation, and possibly extending VAT to flights, both of which would push up the cost of flying.

A big rise in landfill tax, the duty charged for burying waste, from £21 per tonne to as high as £75 per tonne by 2013, was another proposal, as was charges on household goods that are wasteful to import — such as out-of-season fruit flown into the country — or inefficient in energy use, such as standard light bulbs.

Mr Miliband confirmed that discussions about such measures were going on within the Government, in advance of the Pre-Budget Report next month and the Budget next spring. The Environment Secretary refused to discuss them, saying that they should go through the proper process. But he told Sky News: “For 150 years we have pumped carbon into the atmosphere, whether through energy or transport, as if it had no price.

“But in fact it has an environmental price and, as we are learning from Sir Nicholas Stern, it has an economic price as well. And for the future we have to recognise that environmental and economic price of carbon emissions in the way we live and work.” He was referring to a report by Sir Nicholas to be submitted today.

The Treasury reacted coolly to the leaked letter, which was reproduced in The Mail on Sunday, saying that the Chancellor received many such submissions as part of his consultations on the Budget.

It follows a period in which Mr Miliband has moved closer to the Chancellor, whom he has endorsed enthusiastically to replace Tony Blair when the Prime Minister stands down. The Environment Secretary’s aides denied strongly that they were behind the leak.

The debate on green taxes intensified as David Cameron, the Conservative leader, said that he was ready to back higher taxes on cheap flights if necessary, although he added that details would have to wait until nearer to the general election.

Mr Cameron told the BBC One Politics Show: “I don’t actually want to stop people going on a family holiday, to restrict air travel, but we have to look at transport as one of the areas and if that means putting a tax on air travel, then yes, that’s something we’d be prepared to do.”

The Tory leader also sought to personalise the debate by accusing Gordon Brown of developing an interest in the environment only after he himself had made it a personal priority. “Raising the profile of these issues, talking about them, demonstrating through your own party how much you actually care about them, can make a difference,” Mr Cameron said.

“I mean, ask yourself, would Gordon Brown be spending as much time on the environment as he is now if I hadn’t raised the issue so strongly over the last year? I think the answer to that is pretty clear.”

The Conservatives later produced a three-page briefing paper with a graph suggesting that the Chancellor had barely mentioned the subject of climate change before his Budget speech last year, when he suddenly made global warming an important theme.

But Sir Menzies Campbell, the Liberal Democrat leader, attacked the Conservatives for failing to match their campaigning on the environment with tough policies to back it up.

He added: “We have absolutely no option but to deal with the problem of climate change and nothing but hard choices will do it.” At their conference the Liberal Democrats embraced plans for green taxes.

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