Powergen today hiked prices by as much as 24 per cent as it became the latest energy supplier to increase household bills.
The group, which has around six million UK customers and is owned by Germany's E.ON, said electricity tariffs would rise by 18.4 per cent with the bill for gas customers increasing by 24.4 per cent.
It blamed wholesale gas costs, which it said had risen by 70 per cent for gas and 63 per cent for electricity since January 2005.
The latest increases, which are the largest in Powergen's history, add £56 to its average annual electricity bill, with gas customers facing a rise of £107.
Powergen said the latest increases - due to come into force on 10 March - were still below the average for the industry.
It also revealed plans to spend £100 million over the next three years to protect its most vulnerable customers from the impact of the higher costs.
Around 10 per cent of Powergen customers are unaffected by today's announcement as they are currently on capped or fixed-price products.
Nick Horler, managing director of Powergen Retail, said: "We shielded our customers from the impact of these costs for as long as possible, and we continue to ensure that our prices are highly competitive."
Rival suppliers Scottish & Southern Energy, Npower, Scottish Power, EDF and British Gas have already announced or implemented price rises this year.
British Gas, which is the UK's biggest supplier, added 22 per cent to electricity and gas bills on the "bleakest day yet" in two years of spiralling prices.
It later revealed operating profits of £1.51 billion for 2005, but said its residential arm was loss-making in the second half of the year.
Earlier this month, the European Commission and UK regulator Ofgem said the lack of open access across continental energy markets had been a key factor behind the shortfall in gas supplies coming into Britain.Reuse content