EDF has said it is not ready to take on new customers from energy firms that have gone bust due to high gas prices.
Two more firms collapsed on Wednesday, but EDF’s Philippe Commaret said it was already working on moving customers from failed company Utility Point.
Ofgem appoints companies as a “supplier of last resort” for people whose energy company has ceased trading.
Mr Commaret said it was now a “big question” whether the regulator can force firms to take these customers on.
On Wednesday, Pure Planet and Colorado Energy became the latest companies to go bust following a sharp rise in wholesale gas prices this year.
Since September, 11 energy firms have collapsed which has affected nearly two million customers.
EDF has taken on 220,000 customers from Utility Point, which went bust a month ago. In January, it was appointed by Ofgem to take over 360,000 households from Green Network Energy.
Mr Commaret said the issue of whether Ofgem can force larger energy firms to step into that role is “the big question at the moment across the industry”.
“What we are seeing is that the supplier of last resort [process] has worked really well until now and we can be very proud that industry has stepped in in order to help the customers who were in distress,” he told the BBC’s Today programme.
“The question is whether or not we will be able to take that any further and I think that for ourselves our top priority is obviously to maintain the quality of service for customers, not to create any detriment to customers.”
A spokesman for Ofgem said that it can “direct” a company to take on customers from a collapsed supplier but that discussions always take place between the regulator and the new firm.
Energy firms have blamed the price cap on customers’ energy bills for the recent spate of collapses.
Wholesale gas prices have risen by as much as 250% since January and spiked in August. Domestic customers in England, Wales and Scotland on a standard – or default – tariff are protected from sharp rises in energy costs by the price cap.
Mr Commaret said that “all the suppliers are suffering at the moment”.
Commenting on whether EDF will take on customers from Pure Planet or Colorado, Mr Commaret said: “As you can imagine, on-boarding tens of thousands of customers is a challenge for the operations.
“I won’t apply to be supplier of last resort for any further customers before we have ended with the on-boarding of the Utility Point customers.”
Some of the UK’s largest energy companies have been appointed as supplier of last resort to failed firms.
British Gas has taken on a combined 441,000 customers from MoneyPlus Energy, PFP Energy and People’s Energy. Octopus Energy has stepped in to help Avro Energy’s 580,000 customers.
E.On is supplier of last resort to a total of 233,000 domestic customers from Igloo, Symbio and Enstroga. Shell Energy is looking after 255,000 customers from Green Supplier Ltd.
The government has the power to appoint a special administrator – a quasi-temporary nationalisation – to ensure there are uninterrupted energy supplies to domestic customers.