A Guide to Britain's 'Big Six' Energy Suppliers

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The Big 6 are an unofficial grouping of the UK’s biggest suppliers of electricity and gas. While they still hold an undeniable majority in the UK energy market, their percentage of the market has decreased substantially. In the last five years smaller, newer competitors, like Tonik and Octopus Energy, with cheaper prices and stronger customer service have been able to take more and more of the energy market from the Big 6.


Who are the Big Six?

British Gas

British Gas

The largest of the Big Six companies, British Gas, has their roots in the Gas Light & Coke Company, the very first public utilities company in the world. Since then they have been nationalised, then privatised again to eventually form British Gas plc. in 1986.

They began supplying electricity two years later. Decades of marketing, including the famous Tell Sid campaign, has made British Gas a household name within the UK.

British Gas is the biggest energy supplier in the UK. As of Q3 2018, they held 19% of the UK energy market. They supply energy to more than 11 million homes.



SSE was founded in 1998 from the public sector authorities that previously administered regional energy supply: the North of Scotland Hydro-Electric Board and the Southern Electricity Board. They are the largest producer of renewable energy in the UK. In Q3 2018 they had a 13% market share.

In recent years there was a rumored merger between SSE and npower, but it was ultimately scrapped in late 2018.


British Gas

E.ON is the largest investor-owned gas and electricity company in the world. It formed with the merger of two German energy companies, VEBA and VIAG, and began serving British customers after acquiring Powergen.

E.ON has invested largely in social media and renewable energy projects. As of Q3 2018 they held 13% of the UK market share.

There has recently been discussion that E.ON will acquire npower, which would transform the Big Six to the Big Five.



npower began as part of National Power in 1990. Over a series of separations, mergers and acquisitions, it eventually became the German-owned npower we know today.

The company has a large involvement in the charity sector and a partnership with the Macmillan cancer support trust. As of Q3 2018, they held a 9% market share in the UK.

npower is reportedly in the process of being absorbed by E.ON, which, once completed, could end their existence as a separate brand.

EDF Energy


EDF is owned by the French Electricité de France, who entered the UK market in 1998. EDF was the French national supplier until the recent deregulation of the energy market across the channel.

EDF is both the largest supplier by volume of electricity and the largest producer overall of low-carbon electricity in the UK. They’ve made efforts to engage their local communities with eco-friendly events. In Q3 2018 they supplied 8% of the UK market.

Scottish Power

British Gas

Scottish Power is now part of the Iberdrola S.A. Group, based in Bilbao, Spain. Just like SSE, Scottish Power traces their roots to earlier regional energy boards. They’re the UK’s largest generator of wind energy and are investing further in renewable energy.

Here at Selectra, we have found that their customers are particularly loyal to the company, with many customers staying with them for decades.

Big 6 market share

The combined market share of the Big 6 remains impressive. According to Ofgem, in Q3 of 2018 they held around 75% of the UK energy market.

Even more impressive is how much of the market they’ve already lost. As recently as 2009, the Big 6 held a full 100% of the market. Much of that loss has happened in the last five years, leading many people in the industry to believe the Big 6 will need to change their tactics to avoid further decline.

How They Conquered the Market

The UK energy sector has a long history of private companies being nationalised, then re-privatised, and merged with foreign companies. This history has given the Big Six a market advantage, which many critics claim is unfair and harms the consumer.

The Big Six are the companies that were able to absorb what had previously been the national gas and electricity boards, which had been state-run regional monopolies. This gave them a huge head start.

Some of the Big Six companies, particularly British Gas, enjoy a long history and strong name recognition in the UK.

As many people find the idea of switching suppliers a daunting one, they’re hesitant to make the switch to a smaller supplier, even if they could save money in the process. However, this is largely due to large swathes of the British public being misinformed with regards to energy.

There’s lots of myths about the difficulty of switching energy suppliers: you could lose your energy supply, some suppliers have a less reliable supply of energy, etc. But ultimately, none of those things are true. Switching energy suppliers can be a quick and painless way to save money every month!

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We can find the supplier with cheap rates and decent service for your area.

Company profits

While the revenues of Big 6 companies are still much higher than their competitors, their profit margins have begun to decrease over the last few years.

As more customers switched to smaller, newer suppliers to get a better deal, 2018 annual profits fell by 10% to a still whopping £900 million.

More competitive suppliers and more public awareness of different tariff rates have caused many households to switch energy suppliers. This is slowly but surely cutting into the Big 6’s majority of the UK market, which of course has also cut into their profits.

Who owns the Big Six?

It’s worth knowing who ultimately owns the energy suppliers, especially if you’re interested in investing in shares. For example, if you’re interested in buying Scottish Power shares, you’d actually buy shares in Iberdrola, a Spanish multinational.

Although the Big Six are ubiquitous names in the UK energy market, most of them are owned by large foreign multinational energy companies. Only British Gas and SSE are part of British owned companies.

British gas ownership

British Gas is owned by the British Centrica plc, a multinational energy supply company that supplies the UK, Ireland and North America. They’re also the owners of Scottish Gas and Bord Gáis Energy and have recently taken over the Danish company Neas Energy (now named Centrica Energy). Centrica is listed on the London Stock Exchange as CNA.

SSE ownership

SSE (formerly known as Scottish and Southern Energy) does not have a parent company, and is itself the owner of SWALEC, Atlantic and Airtricity, Scottish Hydro, and Southern Electric. It is a Scottish company and trades on the LSE under the name SSE.

Eon details

E.ON (or e·on in their marketing materials) is a holding company based in Essen, Germany. It’s one of the world’s largest investor-owned electric utility companies and supplies energy in over 30 countries. It’s traded on the Frankfurt Stock Exchange as EOAN.

npower owners

npower is currently owned by RWE, a German energy services company. The RWE is traded in the Frankfurt Stock Exchange as RWE. After the failed merger with SSE, npower leadership has stated they now plan to merge npower under E.ON, with possible layoffs.

edf energy owners

EDF is owned by the Électricité de France, a state-owned electricity supply company in France. EDF entered the UK market with the purchases of SEEBOARD Plc, London Electricity Plc, SWEB Energy Plc, coal and gas power stations and a controlling share in British Energy.

edf energy owners

Scottish Power is owned by the Spanish multinational company Iberdrola. Iberdrola operates in dozens of companies and, in addition to Scottish Power, owns the US energy supplier Avangrid and the Brazilian supplier Elektro Holding. Iberdrola is traded in the Bolsa de Madrid (Spain’s largest stock exchange) as IBE.

Concerns & problems with Big 6 Companies

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Until very recently, virtually all UK households were supplied by one of the Big 6 energy companies. This gave the firms little incentive to lower their prices as in the past up-and-coming brands were too small to make a difference.

There have even been accusations that the Big 6 have colluded. (Collusion is when brands agree, tacitly or explicitly, to keep prices high to maintain higher profits.) But all inquiries have found that their actions were completely legal.

Big 6 companies have also been accused of having deliberately confusing tariff rates and policies, and automatically defaulting customers onto more expensive variable tariff plans. The fact is that Big Six companies continue to take advantage of the British public through confusing pricing and billing practices. With customers finally starting to look at smaller companies with more competitive pricing, the Big Six need to think long and hard about how they treat customers.

Energy pricing

The biggest mark against the Big Six is their high prices. All of the six companies have consistently maintained prices significantly higher than their smaller competitors.

Below you can see the difference in price between each company’s standard tariff option compared to the cheapest option on the market. The larger the difference, the more money you could be saving!

Based on our chart, it’s clear that households can save money by switching no matter which of the Big Six supplies their home’s energy. Even British Gas, surprisingly the most competitive of the six, costs £253 more per year than the cheapest option, while EDF customers could save a full £420 by switching!

Reviews: Where do the Big Six stand?

Apart from their higher prices, the Big 6 also suffer from low customer satisfaction. Across the board, customers complain of poor customer service, surprising bill amounts and problems with their apps and online service. npower in particular has an impressively horrible 92% bad rating on Trustpilot.

20 minutes just to get through [...] punted to the 'move in department' [...] no resolve for a simple thing. - Bryn with npower

The one partial exception is EDF, which has a more respectable 3 stars and some positive notes on their customer service.

I've found EDF to be helpful [...] their overall performance and contact centre staff are [...] good. - Darren with EDF

Below you can find the (horrid) Trustpilot average review score for each of the Big Six energy companies:

If you’re wondering how British Gas ended up with 1 star with 32% of their reviews being Excellent, keep in mind that Trustpilot gives greater weight to more recent reviews. These conflicting numbers imply that British Gas’s customer satisfaction has declined over time.

Newer Independent Energy Suppliers

There are now over 60 different suppliers of gas and electricity in the UK. Many of the newer arrivals sport lower tariffs and higher rated customer service than the Big Six companies.

Some of the best ranked companies in terms of customer service and value for money are Tonik Energy, Octopus Energy, and Robin Hood Energy.

Interested in green energy? Companies including Tonik Energy and Bulb guarantee REGO-backed, 100% renewable energy produced electricity tariffs and 5-10% renewable gas tariffs.

If you’re looking for more info on the UK’s smaller energy suppliers, we’ve broken them down in our small suppliers guide.

Why switch providers?



As more and more new energy providers enter the market, consumers are reacting more strongly to higher energy bills. More households are switching away from the Big Six energy companies than ever.


If you’re currently with one of the Big Six Energy companies, there’s a very simple reason to switch: you could be paying less every month, while receiving better service!