Energy companies yesterday gave the clearest signal yet that bills could rise next year, after warning of a "difficult environment" in 2008.
Scottish Gas owner Centrica said higher wholesale gas prices had cut margins in its residential business, which made profits of £533m this year.
ScottishPower and Npower were among those to echo the concerns, amid counter claims from the energy watchdog that rises were unnecessary.
Scottish Gas still expects the business to be profitable but a spokesman for Centrica added: "Looking forward, the high wholesale prices will, if sustained, create a more difficult environment for retail energy suppliers in the UK going into 2008. We will continue to monitor this with regard to future pricing policy."
Scottish Gas was the first major UK energy firm to cut prices earlier this year - sparking a price war among suppliers - but its parent company said that market conditions had become "more challenging" in recent months as wholesale gas costs rise.
Prices have been driven higher by soaring oil costs and European players buying supplies in the more liberalised UK market.
The firm said its move to cut energy bills had won back the 250,000 customers who deserted the firm earlier in 2007 and the company now has 16 million customers in total across the UK.
A spokesman for Npower said last night: "Since April this year the increase in forward wholesale energy costs has been 75% for gas and 78% electricity, as measured by the well-respected Heren Energy Index.
"Despite this, Npower has continued to protect its customers maintaining the price cuts made in April.
"However, in the face of huge fuel costs, and rises in distribution and environmental costs, the pressure on our prices is increasing."
A spokesman at ScottishPower also pointed towards wholesale prices and added it would be "monitoring the position against our competitors".
A spokesman for energywatch Scotland said: "Gas is abundant; there is no scarcity or shortage of gas so there should be absolutely no need for its price to rise.
"However, the season of illwill towards energy consumers now appears to be in full swing with this warning of price rises from Scottish Gas. Consumers must be despondent and fearing the worst as companies again look set to raise bills."
He added: "The apparent race to raise prices is in marked contrast to the industry's failure to act when it comes to cutting the burden of bills for consumers.
"In the last year wholesale gas prices have fallen by 50% and while the industry enjoyed the respite, they were in no hurry to share the benefits with consumers."
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