image source, Getty Imagesimage captionOfgem acknowledged that "this is a worrying time for many people"
Nearly 1.5 million customers have been affected by energy firms collapsing under soaring gas prices.
Avro Energy and Green ceased trading on Wednesday and their 830,000 combined customers face being switched to a new, potentially more expensive, provider.
All affected customers will still receive energy while a new supplier is appointed by watchdog Ofgem.
Neil Lawrence, director of retail at Ofgem, said its "number one priority is to protect customers."
The regulator's price cap also limits how much firms can charge.
But providers have complained that they are unable to pass on rising costs to customers because of the cap on energy bills.
Since wholesale gas prices have started to spike, a number of firms have collapsed.
People's Energy, Utility Point, PfP Energy and MoneyPlus Energy ceased trading in September.
These smaller companies, including Avro Energy and Green Supplier Limited, account for more than five per cent of the UK energy market - about 1.5 million customers.
Mr Lawrence added: "We know this is a worrying time for many people and news of a supplier going out of business can be unsettling."
He reminded customers of the failed companies that the regulator would be appointing a new supplier for them and suggested that it is best not to try to switch in the meantime.
The energy regulator's boss did, however, warn on Wednesday that other suppliers may face a similar fate.
"We've already seen hundreds of thousands of customers affected, that may well go well above that. It's very hard for me to put a figure on it," Jonathan Brearley said in front of the Commons cross-party business committee.
He would not say if the number of customers that would eventually need new suppliers could run into "millions".
What happens if your energy supplier goes bust?
Lisa Barber of consumer rights group Which? said that millions of people may be feeling apprehensive because of speculation that other small companies could fold in the coming days and weeks.
Igloo, for example, has said it is working with restructuring consultants Alvarez & Marsal, although it told the BBC it had not appointed administrators. Bulb, the UK's sixth largest energy company with 1.7 million customers, is also seeking additional financing.
Ms Barber said: "Ofgem will appoint new energy suppliers to take over and protect any credit customers have so they can be reassured they won't be cut off or lose their money. We'd recommend taking a meter reading as soon as possible to ensure the transition is as smooth as it can be."
image source, Getty Images
Smaller providers launched in recent years have been overwhelmed by a spike in the cost of wholesale gas prices as economies have reopened from lockdowns and high demand from Asia pushed down supplies to Europe.
Gas prices are rising all across Europe, but Britain has also been affected by lower winds than usual - denting renewable energy supplies - as well as a recent fire at a National Grid site in Kent.
In the UK, firms had already been hit by a jump in costs even before the recent spike. From more than 70 suppliers in 2018, there are just over 30 now.
Industry sources fear there may be as few as 10 suppliers left by the end of the year.
Ofgem has previously acknowledged that the cost of protecting customers from failing energy providers could lead to higher bills.
Customers on some tariffs are protected from sudden hikes in wholesale gas prices through the energy price cap, which limits how much firms can charge per unit of gas.
The price cap covers 15 million households across England, Wales and Scotland.