By Daniel Hunter
Fresh on the back of British Gas's announcement Npower have also raised the price of their energy bills.
A dual-fuel bill with Npower will go up by 10.4%, with the price rise taking effect as of 1 December. It is the highest rise announced by any supplier so far.
SSE will increase prices by 8.2% from 15 November and British Gas said prices would go up by 9.2% on 23 November.
The Npower increase includes an electricity price rise of 9.3% and a gas price rise of 11.1%. The move will affect 3.1 million customers.
Between August and December last year, the "big six" energy companies outlined price rises of between 6% and 10.8%.
"I know that any increases to household bills are always unwelcome, and this is not a decision that we have taken lightly. We will continue to take steps where we can to reduce the impact of the external influences on energy bills," said Paul Massara, chief executive of Npower.
Npower echoed the view of the other suppliers by saying that the rise was the result of cost increases in delivering energy to homes, fulfilling government schemes and raw materials.
The company said that it "aimed" to make a profit of five pence in the pound, which it regarded as a "fair return" for delivering energy reliably to people's homes and for the risks it has to take on.
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