EDF Energy is to raise the price of gas and electricity for its five million customers, as it has been affected by rising wholesale energy costs.
Gas prices are rising by 19%
From 31 July, its gas prices will rise by 19% and electricity by up to 9.1%.
This is the second time this year that EDF has raised its gas and electricity prices.
EDF is the latest in a long line of energy firms to raise bills, with the firm blaming the increase on mounting wholesale energy costs.
'Prices remained high'
"We have been absorbing some of the costs of increased wholesale prices in the hope they would ease," said Derek Lickorish, EDF Energy chief operating officer.
"However, prices have remained high with little prospect for reduction in the foreseeable future."
Wholesale energy costs have risen by nearly 80% in the past year.
The firm added that it hoped to protect vulnerable customers, by offering a fixed rate energy package to its electricity prepayment customers living in the south of England.
This package will allow people with prepayment meters to avoid price hikes until 2010.
Customers in the company's northern region will see their electricity prices rise by 9.1%, compared to an average price hike of 8% for the rest of the UK.
Ann Robinson, spokeswoman for price comparison website uSwitch.com warned that more pain was in store for UK gas and electricity customers.
"Both Scottish Power and EDF Energy have now raised their prices twice this year... the other suppliers are certain to follow suit over the coming weeks," Ms Robinson said.
Energywatch, the consumer watchdog, described the price hike as having a "wretched sense of inevitability" about it.
It added that prices were now running at historic highs and could get worse over the next few months.