Another three million households face higher energy bills after EDF Energy became the latest supplier to increase tariffs.
The company will raise prices for domestic gas and electricity by 10.8%, meaning its typical dual-fuel bill for a direct debit customer will rise by £122 to £1,251 a year.
EDF, which is the fifth major supplier in recent weeks to announce higher prices, said the change will take effect from December 7. E.ON is the only big supplier yet to announce price rises after it made a promise not to raise tariffs this year.
EDF, which has 3.1 million customers and 5.5 million accounts overall, said its annual dual fuel bill was the lowest of the suppliers to have announced price rises so far.
Companies have blamed the changes on rising wholesale prices and increased running costs, especially for transporting gas and electricity to customers' homes, and the cost of energy efficiency programmes.
EDF director Martin Lawrence said: "We know that customers will not welcome this news and do not want to see prices going up. Our new prices will, however, be cheaper on average than those of all the other major suppliers which have announced standard price rises so far this autumn."
He added the company was taking steps to help vulnerable customers by ensuring that those whom the Government identifies as most in need will automatically benefit from a discount equivalent to being on its cheapest tariff.
Downing Street described the latest price rises as "very disappointing".
"It is up to energy suppliers to explain their prices to their customers," a Number 10 spokeswoman said.
"While we can't control world energy prices, we have been working very closely with the energy companies to make it easier for people to switch to find cheaper deals. We want to ensure customers get the lowest tariffs. That is why we are going to use the law to help people get the best deals."