Energy companies are set to impose another round of punishing price increases on consumers, despite a steep slide in the wholesale price of gas.

Scottish Power is among those expected to announce double-digit price rises for its 5.2 million gas and electricity customers in the coming days.

E.ON, npower and Scottish & Southern Energy (SSE) are also thought to be preparing further rises to household bills.

The increases will be particularly galling for British families already battling with rising mortgage, food and fuel costs, because they follow a sharp fall in wholesale gas prices.

The price of gas for delivery the following day has dropped 32 per cent over the past month, from 69p per therm in early July to close at 47p last night.

Forward gas prices have also fallen. The price of gas for delivery this winter has declined from 104p per therm last month to about 88p per therm.

The decrease has accompanied a near-20per cent drop in the price of crude oil, to which most commercial gas contracts are linked. That touched a high of $147 per barrel on July 11 and is now at about $118.

Andrew Horstead, an analyst at Utilyx, the energy consultancy, said that a supply glut during a period of low summer demand had also forced prices lower. Last week spot gas prices fell to as little as 33p - the lowest for several months.

However Mr Horstead said that further price rises were probably “inevitable” for UK consumers.

“It's not a question of if but when the remaining four increase their prices,” he said.

Energy companies buy their gas using a variety of short and long-term contracts, so some are more exposed than others to fluctuations in wholesale markets. EDF was the first leading energy company to announce price rises for its five million UK customers, of 22 per cent for gas and 17per cent for electricity, two weeks ago.

It was followed last week by British Gas, which increased prices for gas customers in some regions by as much as 44 per cent.

It blamed soaring wholesale energy costs and the need to import more supplies because of the depletion of stores in the North Sea. British Gas also said that it needed to raise prices to ensure it could invest in new sources of low-carbon energy.

A spokesman for Scottish Power declined to comment on potential price rises, while npower said that the company was continuing to monitor the market.

Energy companies have come under fire in recent weeks after MPs on the Commons Business Select Committee issued a damning report on the UK energy market. Peter Luff, its chairman, cited “very real problems in the energy markets at all levels”.

The report accused the so-called Big Six suppliers of operating in a cosy world of minimal price competition. This created an environment where it was “easy for those players to make informed judgments about the behaviour of their competitors. This alone can distort competition without any actual collusion occurring”.

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