Centrica says the increase is due to costs out of its control.
The news comes as the UK’s biggest energy companies seek to play down claims of price manipulation amid profit jumps and price hikes.
SSE, the energy company behind Scottish Hydro, has announced a jump in profits of nearly 40%. The news came just a month after it announced a 9% increase in bills.
SEE also owns Southern Electric and Swalec and is the UK's second-largest generator of electricity.
Now Centrica is planning to raise average prices by 6%.
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The company, which has 15.8m customers, said required investments and carbon reduction targets have added about £50 to the average bill.
It also said wholesale gas prices were now 13% higher this winter than last.
Centrica reported average UK residential gas consumption for the first 10 months of 2012 was 9% higher than for the same period of 2011.
It also reported a decline in average electricity consumption of 1%.
"This reflects colder than normal weather in the year to date following an unusually warm 2011, but also underlying reductions in demand due to energy efficiency measures undertaken by customers," Centrica said.
Commenting on the SSE profit increase, the Unite union dealt a blow to UK energy companies.
Kevin Coyne, Unite national officer for energy, said: "These profits are excessive, especially when price increases have caused more hardship for those customers already struggling to get by.
"The government has washed its hands of all responsibility and left it to the market, which is clearly failing to deliver on price. This Tory government stubbornly refuses to properly regulate the energy industry."
(IT)
