SSE said its average annual dual fuel energy bill would rise by £106 to £1,380 on 15 November.
One industry expert described the move as “the final nail in the coffin for affordable energy”, but SSE said that many costs were beyond its control.
The decision prompted fevered political debate over who to blame for the rise.
Citizens Advice is expecting an “avalanche” of increases but has called on the other energy firms to freeze prices.
“This price rise will be a blow for stretched budgets,” said the charity’s chief executive Gillian Guy.
“I hope other energy firms show an understanding of their customers’ financial situation by not raising their prices this winter.
“Many households are facing a daily battle try to make their frozen incomes cover mounting energy, food and travel costs. Further increases will push people into poverty.”
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