Npower has become the third major energy supplier to unveil a price rise, as its unveiled a 10.4% increase, which would add £139 to an average annual bill.
The energy firm's increase, the highest rise from any supplier announced so far, will take effect from 1 December and will affect two million customers. Npower's price rise comes after SSE announced it would put up prices by 8.2% from 15 November and British Gas would increase theirs from 23 November by 9.2%.
The Npower increase includes an electricity price rise of 9.3% and a gas price rise of 11.1%.
Npower 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 will continue to take steps where we can to reduce the impact of the external influences on energy bills."
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Npower has increased prices by £247 since November 2012. The energy firm's price increases come after Labour leader Ed Miliband pledged to freeze prices for 20 months if his party wins the next election.
But Prime Minister David Cameron branded Mr Miliband's price freeze plan as a "con", saying that he did not have control over the worldwide price of gas.