Gas and electricity supplier Npower is raising energy bills by an average of £64 a year for a million customers.
The average 5.3% dual fuel price hike comes into effect on 17 June and follows earlier rises announced last month by its “Big Six” rivals.
British Gas is increasing prices by 5.5% from 29 May, while EDF is raising electricity prices by 2.7%.
German-owned Npower blamed increases in policy and wholesale energy costs for the increase.
Simon Stacey, managing director, domestic markets at Npower, said: “Announcing this price change today isn’t a decision we’ve taken lightly.”
He said the costs energy suppliers are facing – “particularly wholesale and policy costs which are largely outside our control” – have been on the rise for some time “and we need to reflect these in our prices”.
The 5.3% average price hike is made up of a 4.4% rise in gas prices and a 6.2% increase in electricity.
Mr Stacey pointed out that the price rise would not affect existing customers on a fixed deal, those with a prepayment meter, or customers on the Safeguard tariff.
Stephen Murray, energy expert at MoneySuperMarket, said: “This is a chunky rise from Npower – all we need now is something from SSE and it’s a full house from the Big Six.
“Npower says 60% of its customers won’t be affected but that still means 40% – or one million people – will.”