EDF and E.ON are among several energy groups that are understood to be considering price rises of up to 10 per cent, possibly as early as January. One industry source said: “It is not a question of if, so much as when. Once one goes, they will all go.”

In recent months, energy suppliers have been hit by a combination of rising distribution costs related to infrastructure improvements and soaring prices in wholesale gas markets, which also influence electricity prices.

Since February, annual forward gas prices for 2008 have risen 42 per cent from 33p a therm to 47p a therm - about 10p more than industry forecasts, according to analysts. Spot prices have risen 55 per cent over the past year to about 42p a therm from 27p.

Energy broker Catalyst Consumer Services has forecast that retail energy prices could rise by up to 10 per cent in the new year, a margin that would drive average UK household energy bills through the £1,000 a year mark.

European suppliers such as E.ON are particularly exposed to fluctuations in the continental gas market, which is closely linked to oil prices. Gazprom, for example, is a major supplier of gas to the German group and indexes its gas exports to crude prices. Last month these touched record highs of almost $100 a barrel.

Tim Wolfenden, head of home services at uSwitch.com, yesterday predicted rises of 10 per cent to 20 per cent in UK household bills “in the early part of next year”.

“The bottom line is, if one supplier is feeling the pressure it will pass it on to the consumer,” said Mr Wolfenden. “The floodgates will open.”

While new pipelines from the Continent mean that there is unlikely to be any shortage of gas in the UK this winter, one City analyst claimed that unless there is a sudden slide in wholesale gas prices in the run-up to Christmas, suppliers will be forced to act in the new year to protect profits.

EDF said its prices were “continually under review” and that they would continue to be “competitive”. A spokesman for E.ON said that it was “closely monitoring wholesale power and gas prices” but had no plans to adjust them.

Some suppliers have already lifted niche tariffs. British Gas, Britain’s biggest energy supplier with ten million gas and six million electricity customers, announced on Tuesday that it was increasing the cost of its Market Tracker energy plan, which follows wholesale prices, by up to 15 per cent. Another provider, nPower, is thought to be considering a similar increase in its tracker product in January.

The prospect of further price rises represents a stark reversal in the outlook for UK energy prices from earlier this year, when suppliers announced a series of price cuts after a period of big rises. In March and April, British Gas trimmed gas prices twice, by 17 per cent and 3 per cent.

A spokesman for Centrica, which owns British Gas, said: “It’s too early in the winter to say where wholesale prices will go and therefore what the outlook is for consumer pricing.”

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