The average figure of 8.2%, from November 15, will equate to an average £2 a week increase for typical dual fuel customer
Energy giant SSE is to increase gas and electricity prices by an average of 8.2% from November 15.
The company cited an increase in the cost of buying and delivering wholesale energy as well as Government levies collected through bills for the increase three times the rate of inflation.
SSE, which has around 10 million customer accounts, trading as Southern Electric, Swalec and Scottish Hydro, said the hike equated to an average £2 a week for a typical dual fuel customer.
Will Morris, group managing director of retail, said: "We're sorry we have to do this. We've done as much as we could to keep prices down.
"But the reality is buying wholesale energy in global markets, delivering it to customers' homes, and Government-imposed levies collected through bills - endorsed by all the major parties - all cost more than they did last year."
SSE last put up bills, by 9%, a year ago as its retail operation serving household customers saw profits increase 28% to £410.1 million in the year to March as gas consumption increased by a fifth during a period that included a bitter winter.
Overall pre-tax profits were up from £1.34 billion to £1.41 billion.
But in a trading update last month, SSE revealed it made a loss on its retail operations over the summer after wholesale gas prices rose; buying energy in global markets rising by 4% for a typical dual fuel customer, while paying to use upgraded electricity and gas networks is 10% more expensive.
Government-imposed levies on bills has also risen by 13%.
Customers in the South East will face increases of around 9.7% and at the lower end in the North and southern Scotland will see bills go up 7% while those who use a particularly high proportion of energy at off-peak times may experience a higher percentage increase.
SSE said around 4.4 million household electricity customers and 2.9 million household gas customers in Britain would be affected by the rise. Others are on fixed-price deals.
The average annual standard dual fuel bill, for a customer who pays by direct debit and receives a paper bill, will rise from £1,274 to £1,380.
The issue of rising energy bills have become a key political issue after Labour leader Ed Miliband pledged he would freeze tariffs if elected Prime Minister.
Energy Secretary Ed Davey sought to play down the effect of Government levies - designed to help vulnerable households with energy costs, cut energy waste, and encourage investments in low-carbon generation - on the bill rise.
He said these were far outweighed by the wholesale cost of energy.
Mr Davey said: "This is clearly unwelcome news for customers of SSE. People should take the opportunity now to make sure they are on the best deal available to them."
Today's news suggests this is only the first of a number of major energy suppliers preparing to put prices up this autumn.