Co-operative Energy has scrapped its standard variable tariff (SVT) for customers on fixed deals.
They will no longer be automatically switched to its SVT when their fixed price tariff comes to an end.
It instead switches them to a new fixed tariff, which has no exit fees and runs until May 2019.
SVTs are considered to be much more expensive than other deals available on the market.
A spokesperson for Co-op Energy said: “From December 31st last year, all customers who do not switch to an alternative tariff when their fixed tariff ends are automatically moved onto our new Co-op Fixed Green Energy May 19 v2 fixed-price default tariff, rather than our standard variable rate.
“This ensures that customers who have chosen a fixed tariff in the past get the peace of mind that the price they pay on their new tariff will currently be fixed until May 2019.”
Around five million households will see a £58 increase a year on their energy bills as Ofgem said the level of the safeguard tariff will increase from April.