Consumers were outraged today as npower became the third energy firm to unveil a price rise in less than two weeks, announcing increases of up to 11.1%.
The firm said electricity prices would rise by an average 9.3%, while gas prices will rise by 11.1% from 1 December, adding £141 to the average annual nPower dual fuel bill, which will now stand at £1,493.
Npower said the rises were caused by increases in delivering energy to homes, fulfilling government schemes and the raw materials it uses to generate energy.
Chief executive Paul Massara said: "I know that any increases to household bills are always unwelcome, and this is not a decision that we have taken lightly. We only aim to make around 5p in every pound (5%) in our retail business, which we feel is a fair return for delivering reliable energy to consumers and for the risks that we bear."
It emerged today that gas and electricity prices have increased by 152% over the last decade - four times faster than inflation (38%).
The figures, published by the TUC, were calculated before the latest energy price rises announced by SSE, British Gas and npower.
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Frances O'Grady, TUC general secretary, said: "With people suffering the longest real wage squeeze in over a century these price rises have come into sharp focus. Consumers want action from politicians to tackle the excess profits and undeserved bonuses of the big six energy companies."
On 10 October, SSE became the first of the big six energy firms to raise prices ahead of winter, with the announcement of an average rise in gas and electricity prices of 8.25% from 15 November. British Gas then outraged consumers by announcing average price rises of 9.2% a week later, including an increase of 8.4% for gas and 10.4% for electricity.
Collectively, the three price rises announced to date will affect over 18 million consumers.
The day after British Gas announced its price rises, the firm tried to appease angry customers by answering questions on Twitter - but the conversation was hijacked by incensed consumers who took the energy firm to task for raising prices by almost four times the rate of inflation just before winter.
Commenting on today's price increase announcement from npower, Clare Francis, editor-in-chief at MoneySuperMarket.com, said: "The domino effect has really kicked in. Three down, three more to go. Npower is the third of the Big Six energy firms to announce a price hike and even more UK households are feeling the pressure."
Energy experts advise consumers to switch to a fixed-rate tariff to avoid the price rises. There are deals available that promise to fix prices for the next four winters, such as EDF Energy Blue+ Price Freeeeze; while First Utility has promised there will be no price rise this winter.