Co-op Energy has announced it is increasing its gas and electricity prices by 5.2%.
It will come into effect from 20th August and will affect around 128,000 households on the standard variable tariff.
Customers will see their bills increase by £61 to £1,218 per year – a total of £7.8 million nationwide.
A spokesperson for Co-op Energy said: “As the largest member-owned energy supplier in the UK, our customers are at the heart of everything we do. That is why we do our best to protect them from price fluctuations wherever possible.
“For that reason, we were the first major energy supplier to automatically move customers onto a new fixed-price default tariff rather than our variable tariffs and why we have sought to absorb the significant increases in wholesale energy costs this year. However, this is not sustainable indefinitely and we have therefore reluctantly taken the decision to pass on some of these costs to customers on our Green Pioneer tariff from August 20.”
All the Big Six suppliers have also increased energy tariffs this year.