British Gas has swooped in to supply stranded customers from collapsed energy firms Neon Reef and Social Energy.
It will onboard all 35,500 domestic consumers from both companies.
This switchover is part of Ofgem's Supplier of Last Resort (SOLR) process.
The two firms ceased trading last week.
British Gas will get in touch with former customers from Neon Reef and Social Energy over the coming weeks to help them switch over.
They will need to take a meter reading and provide this to British Gas to make sure they are billed accurately.
Chris O'Shea, group chief executive of British Gas' parents company, Centrica.
He said: "We welcome customers of Neon Reef and Social Energy to British Gas, and we'll ensure the switchover is as smooth as possible. We're a brand trusted by millions and our new customers will benefit from the range of advantages that come with being a British Gas customer, including access to exclusive offers on services like boiler cover, Hive products and British Gas Rewards."
Nearly two million customers have been moved through supplier of last resort processes since September, with 21 energy firms ceasing trading in the past three months.
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Approximately 500,000 have been taken on by British Gas.
Meanwhile, Bulb - the UK's seventh biggest energy firm with 1.7 million customers - has ceased trading.
The average consumer price cap remains set at £1,277 per year for average use, while soaring wholesale costs have risen 250 per cent over the course of the year.
This has left energy suppliers facing hefty losses from both taking on domestic consumers and in maintaining their own businesses.
Scottish Power CEO Keith Anderson recently called for price cap reforms, fearing the market could return to a Big Six scenario.
By City AM
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