Scottish and Southern Energy (SEE) has revealed it will increase its energy prices by 9.4% next month.
It is believed that around 3.6 million customers across the UK will be affected by the rise in their utility bills at the start of December.
Analysts believe that energy costs could increase by as much as £70 a year, which the company has offered up its apologies for.
Alistair Phillips-Davies, energy supply director at SSE, commented: "The last few months have been marked by rising wholesale gas prices and, having absorbed losses in our gas supply business for some time, we cannot delay an increase in retail prices any longer."
Customers in Wales are expected to be the hardest hit, with an estimated 440,000 homeowners likely to be paying higher utility bills over the coming months.
It was recently revealed by npower that a third of Brits fear their boiler breaking down over the winter, leaving them living without heating until they can get it fixed.