Octopus Energy overtook British Gas in late 2023 to become the UK's largest electricity supplier, according to Uswitch's account of the UK's energy supplier market share1. The change followed Octopus's acquisition of Shell Energy's domestic supply business, a process completed on 1 December 20231.
Shell had announced in the summer of 2023 that it would sell its UK domestic energy business to Octopus and exit the market1. First Utility, a challenger brand, had earlier been acquired by Shell and renamed Shell Energy1. Octopus entered the UK energy market in 2016 and grew through a combination of natural growth and acquisitions1. The company claims nearly one million people switched to it during 20241.
By July 2026, Uswitch reports Octopus as the UK's largest energy supplier by market share, supplying 25.7% of electricity customers and 25.9% of gas customers, and as the overall largest energy supplier as of March 20261. British Gas, described as Britain's oldest energy supplier, remains the largest gas supplier as of March 2026 and the second-largest electricity supplier1.
The wider UK energy supplier ranking has been reshaped by exits and takeovers over the past decade. SSE agreed in December 2019 to sell its customer portfolio to OVO, a deal covering 1.5 million customers1. npower moved its customer base to E.ON in 2021, with those customers shifted to the sub-brand E.ON Next1. Uswitch lists E.ON Next as the third-largest supplier as of March 2026, OVO as fourth, EDF as fifth and ScottishPower as sixth1. It adds that OVO is due to be acquired by E.ON in the near future1.
"Octopus overtook British Gas in late 2023 to become the UK's largest electricity supplier"
| Supplier | Position reported by Uswitch |
|---|---|
| Octopus Energy | Largest electricity supplier; largest overall as of March 2026 |
| British Gas | Largest gas supplier as of March 2026; second-largest electricity supplier |
| E.ON Next | Third largest as of March 2026 |
| OVO Energy | Fourth largest |
| EDF Energy | Fifth largest |
| ScottishPower | Sixth largest as of March 2026 |
Why it matters for households
Who supplies a home's electricity does not change how that electricity reaches it. Uswitch states that when a household switches supplier, the supply remains the same, delivered through the same pipes and cables, and only the company charging for the energy changes1. The consolidation described here therefore concerns billing, tariffs and customer service rather than the physical UK energy supply itself.
The shift also affects what happens if a supplier fails. Uswitch says that if a supplier goes out of business, Ofgem moves customers to a different supplier, likely one of the largest firms1. It reports 17 energy suppliers operating in the UK as of April 2026, according to Ofgem1. Uswitch notes that a market dominated by a small number of firms carries a potential for uncompetitive tariffs and higher bills1.
For households weighing a change of supplier, Uswitch says switching requires a postcode and details of the current provider and tariff, and that the old and new suppliers handle the process1. It adds that smaller suppliers often offer deals on par with, or cheaper than, the largest firms, but that concern about smaller companies going out of business is a common reason people do not move1.
What happens next
Uswitch states that OVO Energy is due to be acquired by E.ON in the near future, without giving a date1. No completion date for that deal has been reported.
Sources1 cited
- Big six energy suppliers in the UK - Uswitch, uswitch.com