Renewable energy supplier Pure Planet is to cease trading, regulator Ofgem has said, affecting 235,000 customers.
Colorado Energy has also gone bust, affecting a further 15,000.
“The government and Ofgem expects Pure Planet to sell energy at a price much less than it currently costs to buy,” Pure Planet said in a notice to customers on its website.
“This is unsustainable, and therefore, sadly we have had to make the difficult decision to cease trading.”
It adds: “We’re truly sorry to have let you down.”
Neil Lawrence, director of retail at regulator Ofgem, 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. If you have credit on your account the funds you have paid in are protected and you will not lose the money that is owed to you.
“Ofgem will choose a new supplier for you and while we are doing this our advice is to wait until we appoint a new supplier and do not switch in the meantime. You can rely on your energy supply as normal. We will update you when we have chosen a new supplier, who will then get in touch about your tariff.
“Any customer concerned about paying their energy bill should contact their supplier to access the range of support that is available.”
It comes after Igloo, Symbio and Enstroga ceased trading on 29 September, affecting a combined 233,000 domestic customers.
They followed the failures of People’s Energy, Green Supplier Ltd, Utility Point, PfP Energy, MoneyPlus Energy, and Avro Energy, affecting almost 1.5 million more householders.
Ofgem has also said several players in the sector have not paid into various funds and could have their licences revoked if they do not provide the money.
The chaos in the sector comes amid warnings Britons could see their energy bills rise by 30 per cent next year.
Research agency Cornwall Insight has predicted further volatile gas prices and the potential collapse of even more suppliers could push the energy price cap to about £1,660 in summer.
The forecast is approximately 30 per cent higher than the record £1,277 price cap set for winter 2021-22, which commenced at the start of October.
Ofgem reviews the price cap once every six months, and changes it based on the cost that suppliers have to pay for their energy, cost of policies and operating costs, among other factors.