Britain’s “big six” energy companies have rebuffed calls to cut prices, despite a halving of the wholesale cost of gas and electricity over the past year.

Ofgem, the industry regulator, has been pressing the companies to reduce prices after it was revealed that the companies will be earning £170 from each dual fuel customer over the next year. Over the past three years they have earned an average of £110 per customer per year.

Alistair Buchanan, Ofgem’s chief executive, wrote to the companies last month telling them that “they owe it to their customers to better explain their pricing position to them”.

But replies to Mr Buchanan’s letter published yesterday showed that the big six — British Gas, E.ON, Scottish Power, Scottish and Southern Energy, EDF Energy and RWE — have no plans to trim prices for 26 million households this year. One company even warned that price increases could be pending.

This is despite the fact that the amount they are paying for gas and power on the wholesale market has halved in the past 12 months to the lowest level in almost three years.

Last week forward wholesale prices for 12 months’ delivery, starting next October, were 35.66p per therm for gas and £41.83 per megawatt-hour for electricity, compared with 88.09p per therm and £92.75 per megawatt-hour for the same week in 2008. The average annual household energy bill, however, is £1,239, 18 per cent higher than a year ago, when it stood at £1,048.

Sam Laidlaw, the chief executive of Centrica, the owner of British Gas, even raised the prospect of further retail price rises. He told Mr Buchanan: “Prices \ likely to remain at historically high levels and, in fact, likely to increase as non-commodity costs rise ever upwards.”

Mr Laidlaw pointed out that the wholesale price of gas and electricity accounted for about 60 per cent of consumer bills. The remaining 40 per cent, such as the cost of meeting government targets to produce a third of electricity from renewable sources by 2020, were rising steeply, he said.However, Inenco, a leading energy consultancy firm, rejected this argument. It said that the big six were set to earn an extra £3.4 billion in profits over the next 12 months if they failed to pass on price falls to consumers.

It said that cuts of up to 10 per cent on gas and electricity bills were now fully justified and suggested that this could be just the start of reductions as the competition for customers gathers pace.