A government threat to impose a windfall tax on energy company profits has been attacked as “legalised piracy” by one of the industry's leading representatives.

David Porter, chief executive of the Association of Electricity Producers, which represents Britain's top generating companies, said that plans for such a tax are “just plain daft” at a time when power companies were being urged to make huge investments in low carbon power generation, including nuclear and renewables.

“Windfall taxes are a bad idea - and they are an especially bad idea for an industry that is about to embark on a £30billion investment programme,” Mr Porter said.

“We have a fleet of ageing power stations that have to be replaced with cleaner, greener ones. This is not a good time to be picking the pockets of the companies that are going to have to pay for it.”

Mr Porter's comments came after efforts by Alistair Darling, the Chancellor, to force Britain's energy companies to cut fuel bills for the poor voluntarily by threatening them with a windfall tax on their profits.

There has been mounting anger that household energy bills have risen sharply this year, despite energy groups being in line for a £9 billion windfall from the free allocation of permits under the European Union's greenhouse gas emissions trading scheme. The row was brought into sharp focus last week after Centrica, the owner of British Gas, reported a 50 per cent surge in profits to a record £1.9 billion, one month after raising prices by 15 per cent.

The industry's windfall stems from the cost of electricity increases to reflect the price of permits in the EU's emissions trading scheme, but the companies will be given the permits free during the second phase of the scheme, between now and 2012.

Yesterday, battle lines were being drawn in the debate as Brendan Barber, the TUC general secretary, stepped up his attack on alleged profiteering in the energy industry by calling for a windfall tax to be included in next month's Budget. “These excess profits do not flow from investment, innovation or hard work but simply result from the way that carbon trading has been implemented across Europe,” he said.

He called for a new tax that would be “the centrepiece of a green Budget”, which should show how the Government intended to implement the Stern Review's call for 1 per cent of GDP to be used to tackle global warming.

Malcolm Wicks, the Energy Minister, told The Times last week that he was concerned that energy companies' pricing policies, which reward customers who sign up to internet-only tariffs, could discriminate against the 4.5 million people thought to be in fuel poverty in the UK, including the elderly and low-income groups.The industry argues that rising prices are a consequence of rising wholesale energy costs and increased investment. Tony Ward, a partner at Ernst & Young, said that the knee-jerk imposition of a tax could cut the amount of investment in Britain, which “may do harm to the UK's longer-term carbon emissions goals”.

A spokesman for Centrica said that the company already had 340,000 customers on “social tariffs” that allow poorer members of the community to qualify for reduced bills.