Big Six energy suppliers

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The Big Six were the United Kingdom's largest retail suppliers of gas and electricity. In 2019, the Big Six companies were British Gas, EDF Energy, E.ON UK, Npower, Scottish Power, and SSE.

As of Q3 2019, the Big Six held a combined market share of 70% for electricity supply and 69% for gas supply in Great Britain. They previously held a combined market share across both markets of 100% in 2004.[1][2]

In 2019, a complex merger and asset swap transaction meant that German power giant E.ON absorbed Npower. OVO Energy acquired SSE's domestic retail customers, effective January 2020, but will continue to use the SSE brand for the time being.[3][4]

The companies[edit]


Supplier Customers in the UK (millions) Parent Other divisions and brands Former brands
British Gas 15 Centrica Scottish Gas
EDF Energy 5.7 Électricité de France SEEBOARD, SWEB Energy, London Electricity
E.ON UK 4.6 E.ON Powergen
npower 6.5 E.ON Innogy, Northern Electric, Yorkshire Electricity
Scottish Power 5.3 Iberdrola PPM Energy MANWEB
SSE 9.1 OVO Energy (since 2020) Scottish and Southern, Southern Electric, SWALEC, Scottish Hydro

2014–2016 competition investigation[edit]

In June 2014, energy market regulator Ofgem referred the energy industry to the Competition and Markets Authority (CMA).[7] The authority investigated the "six large energy firms" and published its report in June 2016.[8] For the retail market, the report recommended:[9]

  • Removal of the requirement imposed by the 2014 Retail Market Review that limited suppliers to offering no more than four tariffs
  • Establishment by Ofgem of a database of customers who have been on a "standard variable tariff" for three years or more, which competitors could use to contact those customers
  • A temporary price cap for customers on prepayment meters
  • Measures to support price comparison websites in the energy market.

Consolidation to Big Five[edit]

In 2017, SSE and Npower announced a merger of their retail businesses,[10] but this was scrapped in 2018.[11]

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.[12] This was completed in 2019.[13]

Alternatives to the Big Six[edit]

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.[14] 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.[15] In June 2015, a Cornwall Report stated Opus Energy had broken the dominance of the 'Big Six' energy suppliers in the business market.[16]

The Competition and Markets Authority published an investigation into the energy supply market in June 2016, following a referral by Ofgem in June 2014.[17] 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).[18] 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.[19]

Since 2009, other entrants into the market include a number of new energy companies including Bulb Energy, Good Energy, Ecotricity, and Octopus 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.[20]

Local authority-owned companies[edit]

Three of the alternative energy companies have been owned by local authorities. The first such company since 1948 was Robin Hood Energy, owned by Nottingham City Council, which entered the market in 2015. Bristol Energy, also launched in 2015, was owned by Bristol City Council. Both Robin Hood Energy and Bristol Energy were available to consumers throughout the country until their demise in 2020.

In January 2020, London Power was launched by the Mayor of London. Contrary to the other two companies, it only provides gas and electricity to London homes. London Power is not itself an energy supplier, instead it is a partnership between the Greater London Authority and a providing partner, currently Octopus Energy.[21]

Defunct competitor companies[edit]

By January 2019, ten[22] small energy suppliers had ceased trading or been taken over by others.

Company Ceased Customers (approx.) Customers transferred to
Affect Energy September 2018 22,000 Octopus Energy (acquisition)[23]
Breeze Energy December 2019 18,000 British Gas[citation needed]
Brilliant Energy March 2019 17,000 SSE[24]
Bristol Energy September 2020 155,000 domestic,

4,000 business

Business: Yü Energy[25]Domestic: Together Energy[26]
Economy Energy January 2019 235,000 OVO Energy[27]
ENGIE UK January 2020 70,000 Octopus Energy (acquisition of ENGIE's domestic UK customers) [28]
Extra Energy November 2018 108,000 domestic,

21,000 business

Scottish Power[29]
Flow Energy May 2018 130,000 Co-op Energy (acquisition)[30]

Brand continued until acquired by Octopus in 2019[31]

Future Energy January 2018 10,000 Green Star Energy[citation needed]
GB Energy Supply November 2016 160,000 Co-op Energy (acquisition)[32]

Brand continued until acquired by Octopus in 2019[31]

Green Network Energy January 2021 360,000 EDF[33]
Green Star Energy October 2019 200,000 Shell Energy (acquisition)[34]

Green Star was a subsidiary of Canada's Just Energy

Iresa July 2018 100,000 Octopus Energy[35]
OneSelect December 2018 36,000 Together Energy[36]
Our Power January 2019 31,000 Utilita Energy[37]
Robin Hood Energy September 2020 112,000 domestic,

2,600 business

British Gas[38]
Simplicity Energy January 2021 50,000 British Gas Evolve[39]
Solarplicity August 2019 60,000 EDF Energy[40]
Spark Energy November 2018 290,000 OVO Energy[41]
Tonik Energy October 2020 130,000 Scottish Power[42]
Toto Energy October 2019 134,000 EDF Energy[43]
Usio Energy October 2018 7,000 First Utility[44]
Yorkshire Energy December 2020 74,000 Scottish Power[45]


  1. ^ "Electricity supply market shares by company: Domestic (GB)". Ofgem. 1 January 2020. Archived from the original on 6 February 2020. Retrieved 6 February 2020.
  2. ^ "Gas supply market shares by company: Domestic (GB)". Ofgem. 1 January 2020. Archived from the original on 6 February 2020. Retrieved 6 February 2020.
  3. ^ "New UK energy giant created in SSE-Ovo deal". BBC New: Business. 13 September 2019. Retrieved 16 September 2019.
  4. ^ "SSE and OVO". Retrieved 22 January 2020.
  5. ^ "UK Power". 8 November 2017. Retrieved 8 November 2017.
  6. ^ E.On profits hit by UK customer woes. BBC News, 9 May 2017.
  7. ^ Macalister, Terry (26 June 2014). "Ofgem puts big six energy suppliers under CMA spotlight" – via The Guardian.
  8. ^ "Energy market investigation" (PDF). Competition and Markets Authority. 24 June 2016. Retrieved 8 October 2020.
  9. ^ "The CMA's final report in the energy market investigation". Walker Morris. 8 July 2016. Retrieved 8 October 2020.
  10. ^ "SSE confirms merger with Npower". BBC News. 8 November 2017. Retrieved 27 March 2018.
  11. ^ Vaughan, Adam (17 December 2018). "SSE and npower scrap merger plan amid 'challenging conditions'". The Guardian. Retrieved 29 December 2018.
  12. ^ Vaughan, Adam (28 December 2018). "Job fears for npower staff, with ownership transferring to E.ON". The Guardian. Retrieved 29 December 2018.
  13. ^ "Eon closes deal for Innogy shares from RWE". ReNews. 19 September 2019. Retrieved 1 December 2019.
  14. ^ "Utility Warehouse buys 770,000 customer accounts from npower in £218m deal".
  15. ^ "First Utility becomes first independent energy company to reach milestone of 1m customer accounts and pledges 1% of profits to charity".
  16. ^ "Opus breaks big six dominance of business energy market". Utility Week. 11 August 2015. Retrieved 23 July 2019.
  17. ^ "Ofgem refers energy market for CMA competition investigation". Utility Week. 26 June 2014. Retrieved 5 May 2019.
  18. ^ "Utilita Energy Limited: Annual Report 2017". Companies House. 31 March 2017.
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  20. ^ "We support community energy". Co-operative Energy. Archived from the original on 12 June 2018.
  21. ^ "London Power". London City Hall. 29 October 2019. Retrieved 6 February 2020.
  22. ^ 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.
  23. ^ Bairstow, Jonny (5 September 2018). "Octopus Energy buys Affect Energy". Energy Live News. Retrieved 5 May 2019.
  24. ^ "Ofgem appoints SSE to take on customers of Brilliant Energy". Ofgem. 14 March 2019. Retrieved 5 May 2019.
  25. ^ Hailstone, Jamie (10 August 2020). "Bristol City Council sells off part of energy business". Environment Journal. Retrieved 11 August 2020.
  26. ^ "Bristol Energy: Troubled company sells off domestic customer base". BBC News. 8 September 2020. Retrieved 9 September 2020.
  27. ^ "Ofgem appoints OVO Energy to take on customers of Economy Energy". Ofgem. 11 January 2019. Retrieved 5 May 2019.
  28. ^ "ENGIE UK announces the sale of its residential energy supply business to Octopus Energy". ENGIE UK. 20 January 2020. Retrieved 22 January 2020.
  29. ^ "Ofgem appoints Scottish Power to take on customers of Extra Energy". Ofgem. 24 November 2018. Retrieved 5 May 2019.
  30. ^ "Co-op Energy acquires Flow". Co-op Energy. 2 May 2018. Retrieved 6 September 2019.
  31. ^ a b Stoker, Liam (29 August 2019). "Octopus Energy and Co-op Energy confirm major 'strategic energy partnership'". Current News. Retrieved 6 September 2019.
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  33. ^ "Green Network Energy Customers: Your questions on new supplier EDF". Ofgem. 30 January 2021. Retrieved 13 February 2021.
  34. ^ Stoker, Liam (9 October 2019). "Shell Energy lands £10.5 million Green Star Energy acquisition deal". Current News. Retrieved 11 October 2019.
  35. ^ Knapman, Helen (1 August 2018). "Octopus Energy to take on 100,000 Iresa customers". Moneywise. Retrieved 5 May 2019.
  36. ^ "Ofgem appoints Together Energy to take on customers of OneSelect". Ofgem. 13 December 2018. Retrieved 5 May 2019.
  37. ^ "Ofgem appoints Utilita to take on customers of Our Power". Ofgem. 30 January 2019. Retrieved 5 May 2019.
  38. ^ "Nottingham council 'sorry' as Robin Hood Energy collapses". BBC News. 4 September 2020. Retrieved 7 October 2020.
  39. ^ "Simplicity Customers: Your questions on new supplier British Gas Evolve". Ofgem. 30 January 2021. Retrieved 13 February 2021.
  40. ^ "Solarplicity customers: Your questions on new supplier EDF". Ofgem. 16 August 2019. Retrieved 18 August 2019.
  41. ^ "Ofgem appoints OVO Energy to take on customers of Spark Energy Supply Limited". Ofgem. 27 November 2018. Retrieved 5 May 2019.
  42. ^ "Ofgem appoints Scottish Power to take on customers of Tonik Energy Ltd". Ofgem. 9 October 2020. Retrieved 14 October 2020.
  43. ^ "Ofgem appoints EDF Energy to take on customers of Toto Energy". Ofgem. 26 October 2019. Retrieved 29 January 2020.
  44. ^ "Ofgem appoints First Utility to take on customers of Usio Energy". Ofgem. 18 October 2018. Retrieved 5 May 2019.
  45. ^ Lempriere, Molly (7 December 2020). "ScottishPower takes on collapsed supplier Yorkshire Energy's customers". Current News. Retrieved 8 December 2020.