Together Energy has become the 26th energy company in just five months to be buried under the weight of soaring gas prices.
The business has exited the market, regulator Ofgem said, leaving its 176,000 household customers without an energy supplier.
Ofgem has taken on the job to find them a new home with one of Together’s rivals.
The firm also owned Bristol Energy.
The energy watchdog’s head 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 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.”
Ofgem has so far managed to find new homes for all energy customers left in the lurch by a failing supplier except Bulb, which had so many customers that the watchdog and the Government feared no other supplier could step in without being at risk themselves.
Bulb was granted a £1.7 billion loan from the Government and is being run under special administration.
Energy bills are expected to soar in April when the energy price cap rises.
Analysts believe they could reach around £2,000 per year for an average household – more than £700 higher than today.
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