A new player in the UK energy market is to be created after RWE npower agreed a deal to offload 770,000 customer accounts.
They form part of npower's Electricity Plus and Gas Plus subsidiaries, which were sold today for £218 million to Telecom Plus, a supplier of energy and telephony services trading as Utility Warehouse.
Today's deal is the result of new rules from Ofgem limiting the number of tariffs on offer to domestic customers to a maximum of four.
As Utility Warehouse already manages the brands on behalf of npower, the sale will allow the two companies to continue to offer their customers up to four tariffs under their respective brands.
It will also meet demands for greater competition in the industry at a time of rising energy prices.
Npower, which is part of Germany's RWE Group, currently has 5.4 million customer accounts.
RWE npower chief executive Paul Massara said: "In one move we have helped to create the biggest independent competitor in Britain's household energy supply market.
"This is good for competition and good for consumer choice. Today's announcement shows that Britain is well on the way to having a Big Seven rather than a Big Six."
The company said the deal boosted its medium-term target of supplying gas, electricity, fixed-line telephony, mobile telephony and broadband to more than one million customers.
The deal, which will not result in any change to customer service and contracts, is expected to complete by early January.