Big Six energy suppliers
As of Q3 2018, the Big Six held a combined market share of 75% for electricity supply and 73% for gas supply in Great Britain. They previously held a combined market share across both markets of 100% in 2004.
|Supplier||Customers in the UK (millions)||Parent||Other divisions and brands||Former brands|
|British Gas||15||Centrica||Scottish Gas|
|EDF Energy||5.6||Électricité de France||SEEBOARD, SWEB energy & London Electricity|
|npower||6.5||Innogy||Innogy, Northern Electric, Yorkshire Electricity|
|Scottish Power||5.3||Iberdrola||PPM Energy||MANWEB|
|SSE||9.1||none||Scottish and Southern, Southern Electric, SWALEC & Scottish Hydro|
Possible consolidation to Big Five
Just after the failed SSE-Npower merger in late 2018, it was reported that a consolidation to the Big Five would still occur, as Npower would be acquired by default by E.on due to the already-planned asset swap by the respective German parents, innogy and E.ON. 
In June 2014, energy watchdog Ofgem referred the energy industry to the Competition and Markets Authority (CMA). The 18-month investigation is to conclude whether the big six have been profiteering and should be broken up.
Alternatives to the Big Six
In December 2014, Utility Warehouse, part of FTSE 250-listed company Telecom Plus became the UK's biggest independent energy supplier through a £218m deal to buy 770,000 existing customers from npower. In September 2014, First Utility (since rebranded as Shell Energy) announced it was the first independent utility supplier to reach the milestone of 1m customer accounts for gas and electricity – the equivalent of 550,000 customers, which made it the seventh-largest energy supplier in the UK and the country’s biggest independent energy provider.
The Competition and Markets Authority published an investigation into the energy supply market in June 2016, following a referral by Ofgem in June 2014. The report identified 34 suppliers of both electricity and gas to households, and described the three largest suppliers outside the Big Six as "mid-tier suppliers"; these were First Utility, Ovo Energy and Utility Warehouse. Other significant suppliers (each with more than around 1% market share) were Co-operative Energy, Extra Energy and Utilita Energy (specialising in pre-pay customers). The combined market share of suppliers outside the Big Six had increased from less than 1% in 2011 to around 13% in the first quarter of 2016.
Since 2009, other entrants into the market include a number of new energy companies including Bulb Energy, Good Energy, Ecotricity, LoCO2 Energy, Flow Energy, Spark Energy and Octopus Energy; and, in 2015, the first local authority-owned energy company since 1948: Robin Hood Energy. Many of these newer entrants are seeing significant growth in customer numbers, in part due to their greater commitment to renewable energy and, in the case of Co-op Energy, community renewable energy projects.
Defunct competitor companies
By January 2019, ten small energy suppliers had ceased trading or been taken over by others.
|Company||Ceased||Customers (approx.)||Customers transferred to|
|Affect Energy||2018||22,000||Octopus Energy (acquisition)|
|Economy Energy||2019||235,000||Ovo Energy|
|Extra Energy||2018||108,000 domestic, 21,000 business||Scottish Power|
|Future Energy||2018||10,000||Green Star Energy|
|GB Energy Supply||2016||160,000||Co-op Energy|
|Our Power||2019||31,000||Utilita Energy|
|Spark Energy||2018||290,000||Ovo Energy|
|Usio Energy||2018||7,000||First Utility|
- "Electricity supply market shares by company: Domestic (GB)". Ofgem. January 2019. Retrieved 2019-02-17.
- "Gas supply market shares by company: Domestic (GB)". Ofgem. January 2019. Retrieved 2018-02-17.
- "UK Power". 2017-11-08. Retrieved 2017-11-08.
- E.On profits hit by UK customer woes. BBC News, 9 May 2017.
- "SSE confirms merger with Npower". BBC News. 2017-11-08. Retrieved 2018-03-27.
- Vaughan, Adam (17 Dec 2018). "SSE and npower scrap merger plan amid 'challenging conditions'". The Guardian. Retrieved 29 December 2018.
- Vaughan, Adam (28 Dec 2018). "Job fears for npower staff, with ownership transferring to E.ON". The Guardian. Retrieved 29 December 2018.
- Macalister, Terry (26 June 2014). "Ofgem puts big six energy suppliers under CMA spotlight" – via The Guardian.
- "Utility Warehouse buys 770,000 customer accounts from npower in £218m deal".
- "First Utility becomes first independent energy company to reach milestone of 1m customer accounts and pledges 1% of profits to charity". www.first-utility.com.
- "Ofgem refers energy market for CMA competition investigation". Utility Week. 2014-06-26. Retrieved 2019-05-05.
- "Utilita Energy Limited: Annual Report 2017". Companies House. 31 March 2017.
- "Energy market investigation: Final report" (PDF). Competition & Markets Authority. GOV.UK. 24 June 2016. pp. 24, 388. Retrieved 5 May 2019.
- Stoker, Liam (25 January 2019). "Octopus Energy handed £13.2 million to cover Iresa debts as tenth supplier goes bust". Current News. Retrieved 5 May 2019.
- Bairstow, Jonny (5 September 2018). "Octopus Energy buys Affect Energy". Energy Live News. Retrieved 5 May 2019.
- "Ofgem appoints SSE to take on customers of Brilliant Energy". Ofgem. 14 March 2019. Retrieved 5 May 2019.
- "Ofgem appoints Ovo Energy to take on customers of Economy Energy". Ofgem. 11 January 2019. Retrieved 5 May 2019.
- "Ofgem appoints Scottish Power to take on customers of Extra Energy". Ofgem. 24 November 2018. Retrieved 5 May 2019.
- "Energy firm shambles that has fuelled your fury..." This is Money. 2 October 2018. Retrieved 5 May 2019.
- "GB Energy Supply". gbenergysupply.co.uk. Retrieved 5 May 2019.
- Knapman, Helen (1 August 2018). "Octopus Energy to take on 100,000 Iresa customers". Moneywise. Retrieved 5 May 2019.
- "Ofgem appoints Together Energy to take on customers of OneSelect". Ofgem. 13 December 2018. Retrieved 5 May 2019.
- "Ofgem appoints Utilita to take on customers of Our Power". Ofgem. 30 January 2019. Retrieved 5 May 2019.
- "Ofgem appoints Ovo Energy to take on customers of Spark Energy Supply Limited". Ofgem. 27 November 2018. Retrieved 5 May 2019.
- "Ofgem appoints First Utility to take on customers of Usio Energy". Ofgem. 18 October 2018. Retrieved 5 May 2019.