British Gas will add over £120 to annual fuel bills in a 9.2% hike from November 23, as it increase electricity and gas prices by 10.4% and 8.4% respectively.
Nearly eight million households stand to be affected by British Gas' price rise, which comes after SSE, the UK's second largest energy supplier, unveiled an 8.2% price hike.
Ed Miliband promised to freeze bills until 2017 if Labour wins the next general election. British Gas' announcement will add over £120 a year to the average dual fuel bill.
Energy secretary Ed Davey said: “This is extremely disappointing news for British Gas’s customers, and the company will need to justify this decision openly and transparently."
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Ian Peters, British Gas managing director of Residential Energy, suggested that the firm's price rise did not mean energy bills would have to go up too as customers could be more energy efficient.
"The amount you pay depends not just on the price, but on how much gas and electricity you use. Energy efficiency is making a real difference. We’ve already provided three million customers with insulation, help and advice in managing their bills and keeping their homes warmer for less."