Nothing bolsters Sarah Palin’s credentials among her fans more than her attacks on “big oil”. But the oil industry is retaliating, describing tax increases and fighting rhetoric as “politically astute, but economically dumb”.

There was always going to be tension between the two ends of a message that seeks both to project Mrs Palin as a maverick willing to take on fat-cat corporations and to satisfy a Republican desire for cheaper petrol – not for nothing is the chant at Republican rallies “Drill Baby Drill”.

Campaigning in Virginia yesterday, Mrs Palin repeated her mantra: “In Alaska I broke the lobbyist and special interests that had controlled big oil. We are going to make this nation energy-independent.” Last week she told the Republican convention: “In a McCain-Palin administration, we’re going to lay more pipelines.”

However, energy experts say that in challenging BP, Conoco Philips and Exxon Mobil Mrs Palin may have gone too far, driving billions of dollars out of Alaska and jeopardising the goal of energy independence.

Sources inside the companies told The Times that taxes introduced by Mrs Palin had led them to shelve two multimillion-dollar projects and cancel plans to explore new drilling areas. “They would have produced millions of barrels of oil a year,” one said. “Palin’s taxes were popular. But economically they didn’t make sense. She has behaved like the worst Democrats.”

Mrs Palin has raised taxes on oil profits and given $1,200 rebates to consumers – an idea John McCain has opposed at federal level. She has given $500 million to a Canadian company to build a gas pipeline that the main holders of the state’s gas reserves boycotted. And she has become embroiled in a legal battle over rights to one of the state’s richest gas deposits.

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