Eon is set to become the UK's largest energy supplier after agreeing a deal to buy the retail arm of Ovo - reportedly for as much as £600million.
The deal, which is officially for an undisclosed figure - although the Financial Times reports it could be worth £600million, will see Ovo's 4 million UK customers added to Eon's existing 5.6 million.
The TImes reports analysts at Bernstein have said this would make Eon the UK's largest supplier, overtaking Octopus Energy.
While the deal has still to be rubberstamped, Cornwall Insight has indicated it would mean that 90% of the UK household energy market is held by just five companies.
Consumer group Which? has told Ovo customers not to panic amid the takeover, with existing tariffs to be honoured and services unaffected.
Emily Seymour, energy editor at Which?, said: "If you're an Ovo customer, don't panic, your gas and electricity supply will continue as usual.
"E.On have assured customers that existing tariffs will be honoured in full and service will continue unchanged. You don't need to do anything and you're still able to switch supplier if you wish."
FSTE100
The UK's flagship share index, the FTSE 100, was down 98 points at 10,155 shortly after opening this morning.
Brent crude oil futures were up 1.80%, siting at $106.38 a barrel this morning.
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