Two smaller energy companies have ceased trading.
Whoop Energy and Xcel Power have gone bust and alerted Ofgem of their decision.
Whoop Energy supplies 50 households and 212 businesses, while Xcel is used by 274 businesses, reports The Mirror.
A statement on the Whoop website said: "Whoop Energy is ceasing to trade. Ofgem, the energy regulator, is appointing a new supplier for its customers."
Xcel Power said: "Xcel Power Limited is ceasing to trade."
Dozens of energy firms have gone out of business over the past year due to a rise in gas prices.
Due to a price cap set by Ofgem, energy suppliers cannot pass all of this cost on to consumers.
As a result, many energy firms are selling power for less than it costs them to buy it.
Ofgem director of retail Neil Lawrence said: "Ofgem's number one priority is to protect customers. We know this is a worrying time for many people and news of a supplier going out of business can be unsettling.
"I want to reassure affected customers that they do not need to worry, under our safety net we'll make sure your energy supplies continue."
Ofgem's advice to affected customers of Whoop and Xcel is: "Wait until a new supplier has been appointed and you have been contacted by them in the following weeks before looking to switch to another energy supplier.
"Take a meter reading ready for when your new supplier contacts you.
"This will make the process of transferring customers over to the chosen supplier and honouring any funds that domestic customers have paid into their accounts, where they are in credit, as smooth as possible."
