Octopus Energy and Co-op Energy have signed a deal which will see the former take on more than 300,000 new customers.
The supplier will take ownership of the customers of all three energy supply brands owned by Midcounties Co-operative, including Co-op Energy, Flow Energy and GB Energy, although the Co-op Energy brand will remain.
The move is the fourth significant transaction for the firm in the last year, which now has a customer base of more than one million people.
Octopus Energy has promised all existing customers will pay equal or lower prices going forward.
The partnership, which was completed for an undisclosed sum, will also see the creation of a joint venture to develop and support the UK’s community energy market.
Greg Jackson, CEO of Octopus Energy, said: “This acquisition and our ongoing partnership with Midcounties is another step on the road to improving the domestic energy market for good.
“Our renewable energy supply and outstanding technology is now delivering award winning service to over a million homes in the UK with 100% green electricity as standard.”