Octopus Energy completed its purchase of Shell Energy's UK domestic supply business on 1 December 2023, according to Ofgem's Smart Export Guarantee annual report for SEG Year 4, which states that "Shell Energy was officially acquired by Octopus on 1st December 2023"1. The consumer body Citizens Advice lists the same transaction in its table of supplier takeovers, giving the date as December 20232. The comparison service Uswitch records that Shell announced the sale of its domestic energy business in the summer of 2023 and that "that process was completed on 1 December 2023"3. Which? states simply that "Shell Energy was bought by Octopus Energy in December 2023"4.
The deal followed a period of consolidation in which several large customer books changed hands. Uswitch notes that SSE agreed in December 2019 to sell its customer portfolio to OVO, and that npower moved its customer base to E.ON in 2021 under the E.ON Next brand3. Citizens Advice lists Bulb's customers moving to Octopus in December 2022, and UK Energy Incubator Hub customers also moving to Octopus in July 20222. Ofgem's report refers to "Octopus' complete acquisition of Bulb in June 2023"1, a date that differs from the December 2022 figure given by Citizens Advice; the two sources do not agree on when that transfer completed.
On scale, Uswitch reports that Octopus overtook British Gas in late 2023 to become the UK's largest electricity supplier, and that as of March 2026 it had become the UK's overall largest energy supplier, supplying 25.7% of electricity customers and 25.9% of gas customers3. Uswitch also reports that Octopus claims nearly one million people switched to it during 20243. Which?'s January 2026 survey of 11,945 energy customers placed Octopus Energy on a total score of 74%, with a customer score of 79% and an assessment score of 69%, and named it a Which? Recommended Provider for the ninth year in a row4.
For households that generate their own electricity, the takeover had a direct consequence. Ofgem's report records that Shell Energy had offered Smart Export Guarantee tariffs, and that support under one such tariff ended: "It has since been replaced by a tariff with the same name but a corrected rate"1. The same report notes that SEG tariff support connected to the change ended by the end of January 20241. The SEG requires licensed suppliers to offer at least one export tariff paying above 0p/kWh to eligible small-scale generators, and Ofgem reports 42 tariffs from 13 licensees during SEG Year 4, up from 39 the previous year, with 21 bundled and 21 unbundled1.
Why it matters for households
A change of supplier does not change the physical supply: gas and electricity continue to arrive through the same pipes and cables, and only the company charging for them changes3. Citizens Advice states that households keep their gas and electricity when a supplier is bought or goes out of business, and that they will normally be told when their account is being moved2.
For a home with solar panels or other small-scale generation, the supplier matters more than for a plain import customer, because the export tariff is set by the supplier rather than by government. Ofgem describes the SEG as "a licensee-led initiative since its launch on 01 January 2020", meaning rates, contract lengths and conditions are commercial choices1. A takeover can therefore change the rate a generating household is paid, or the conditions attached to it, even where the tariff keeps its name1. Ofgem reports that from SEG Year 5 it "will be undertaking enhanced compliance activity to ensure SEG licensees are complying with their obligations"1.
What happens next
Ofgem's report sets out no further steps specific to Shell Energy customers beyond the end of SEG tariff support by the end of January 20241. Uswitch reports that OVO Energy is due to be acquired by E.ON in the near future, without giving a date3.
Sources4 cited
- SEG Annual Report - SEG Year 4, ofgem.gov.uk
- Check who's taken over your energy supply - Citizens Advice, citizensadvice.org.uk
- Big six energy suppliers in the UK - Uswitch, uswitch.com
- Best Energy Suppliers 2026: Which? Energy Company Survey Results - Which?, which.co.uk