Four more small British energy suppliers have stopped trading, regulator Ofgem said on Tuesday, taking the number that have gone bust since the start of September to 17.
Many British energy companies, often supplying both gas and electricity to homes and businesses, have struggled with soaring wholesale energy costs, because the regulator's price caps limit how much of the increases can be passed on to customers.
The latest four to cease trading are Omni Energy, MA Energy, Zebra Power and Ampoweruk. They have about 23,700 domestic and non-domestic customers, who will be found new suppliers, Ofgem said.
"In recent weeks, there has been an unprecedented increase in global gas prices which is putting financial pressure on suppliers," Ofgem said.
"Ofgem is working closely with government and industry to make sure customers continue to be protected this winter."
About 2 million customers have been forced to change energy companies.
Customers' potential new energy costs will be covered by the regulator's price cap, but if they were on cheaper fixed tariffs they may have to pay more with their new supplier.
The cap is updated twice a year and rose by between 12 and 13 per cent from the start of October. But wholesale prices have risen far more since that cap was set in August.
Ofgem last week said it would examine whether the cap reflected the costs and risks for energy suppliers, and a decision on any changes would be published in February, when the next price cap level will be announced.