Dual fuel customers will have to pay 6% more for their gas and electricity from 31st August, increasing bills to £1,128 a year.
The standard variable electricity and gas tariffs will rise by 6.1% and 6% respectively.
The Big Six supplier said wholesale prices have increased by 13% since April, when it announced its previous price rise that came into effect last month.
It added that is due to a number of factors, including the ‘Beast from the East’ reducing gas storage stocks over the winter, compounded by global oil markets feeding into higher UK wholesale energy prices.
The price rise will affect around 40% or 1.3 million customers and those on fixed, prepayment or the safeguard tariffs will not see any changes.
Managing Director Beatrice Bigois said: “We know that another price rise will not be welcome and we had hoped that our limited changes announced in April would be enough. However, energy costs have continued to rise significantly and despite our best efforts to absorb some of these by reducing the costs within our control – sadly we can no longer sustain this.
“Customers who wish to avoid this increase will be encouraged to choose one of our fixed price tariffs when we write to them later this month.”Orginal Source