Who are the Big Six Energy Suppliers in the UK?

Who are the Big Six Energy Suppliers in the UK?

Big six energy

The UK energy market is dominated by six major suppliers who together control 77% and 76% of the electricity and gas markets. Together they are known as the "Big Six" and include household names such as British Gas and E.ON. However, in recent years the Big Six have lost millions of customers thanks to the rise of over 60 smaller independent suppliers.

The Big 6 Suppliers

British Gas

Founded in 1997, British Gas are the UK's largest gas and electricity supplier with around 13 million customers. British Gas supply the highest percentage of renewable energy (43%) of all the Big Six and also had the best customer service record and fewest complaints in 2018.


The second largest supplier with around 7.3 million customers are SSE plc. Founded in 1998, they are based in Scotland but supply gas and electricity to customers across the UK and Ireland. They also rank second in terms of renewable energy supply, with around 21% of their energy sourced from renewables.


E.ON are a global energy company based in Germany. The UK arm of E.ON was set up in 1989, originally named Powergen but were rebranded as E.ON in 2007. E.ON supplies around 7 million customers in the UK and they also own and operate renewable energy infrastructure including wind farms and biomass power stations.


EDF is a subsidiary of its French parent company Électricité de France. EDF launched in the UK in 2002 and has around 5.7 million customers. EDF's energy supply is sourced mostly from nuclear energy (71.2%) and they supply the least amount of renewable energy (11.7%) of all the Big Six.

Scottish Power

The fifth largest energy company in the UK with around 5.2 million customers is Scottish Power. Originally founded in 1990, they were taken over in 2006 by Iberdrola, a Spanish energy company and now serve around 10% of the UK's energy market.


The smallest of the Big Six is Npower which was founded in 2002, originally under the name Innogy plc. They currently supply around 4 million customers. Npower offer the third highest percentage of renewable energy (18.7%) between the Big Six - behind British Gas (43%) and SSE (21%) respectively. Npower also specialises in renewable energy for business.

Big Six Market Shares

British Gas remain the largest electricity and gas supplier, with a 20% share of the retail electricity market and 30% of the gas market. The next biggest energy supplier in the UK is SSE, followed by EON, EDF and Scottish Power. Npower take sixth position with a share of 9% of the electricity market and 8% of the gas market.

Although British Gas remain the UK's biggest supplier, their market share has dropped significantly from 25% in 2013. The rest of the big six have also lost market share over the past five years due to the rise of smaller energy suppliers and the increase in customers switching through comparison services such as Selectra UK.

Electricity Market Share
(April - June 2018)
Gas Market Share
(April - June 2018)
1 British Gas 13m 20% 30%
2 SSE 7.3m 14% 11%
3 E.ON 7m 13% 11%
4 EDF 5.7m 11% 8%
5 Scottish Power 5.2m 10% 8%
6 Npower 4m 9% 8%
  Totals 42.2m 77% 76%

Source: Ofgem.

Big Six Fuel Mix - How much Renewable Energy do they offer?

British Gas offers the largest share of renewable energy in their fuel mix (43%), followed by SSE (21%) and Npower (18.7%) respectively.

Thankfully, all the Big Six suppliers have been increasing their supply of green energy in recent years whilst reducing their usage of coal, with no supplier including more than 10%.

When it comes to nuclear energy, EDF Energy are by far the biggest nuclear energy suppliers with a huge 71.2%. The rest however do not rely on nuclear much, especially SSE who only use 5%.

Natural gas also contributes a major element in the Big Six's fuel mixes, with most suppliers sourcing between 37% and 66% of their energy from natural gas. The exception to this is EDF who only use 9.4%.

Overall then, unlike many green suppliers who offer 100% renewable energy, the Big Six still have a way to go to be as green as their smaller rivals. But if you're keen on choosing one of the Big Six AND going green, British Gas are your best bet!

  British Gas EDF Energy E.ON Npower Scottish Power SSE
Renewable 43% 11.7% 16.7% 18.7% 15% 21%
Coal 7% 7.6% 10.1% 9.8% 7% 7%
Natural gas 37% 9.4% 53.5% 52.3% 66% 65%
Nuclear 11% 71.2% 16.2% 15.9% 10% 5%
Other 2% 0.2% 3.5% 3.3% 2% 2%

Source: Electricity.info

The Big Six's Electricity and Gas Prices in 2018

Big Six Electricity and Gas Prices 2018

To compare the prices of the Big Six, we gathered quotes from each of their standard variable tariffs. Using the UK's average household usage figures - 3,100kWh of electricity and 12,500kWh of gas per year, we used the same London postcode to compare prices as closely as possible.

As you can see below, the Big Six actually charge similar rates for gas and electricity on their standard tariffs. EDF Energy appears to be the most expensive supplier among the Big Six at around £1,305 per year for the average 2 bed house in London. British Gas offered the cheapest quote at £1,120, a difference of £185 per year.

Supplier Avg. per year (Elec.) Avg. per year (Gas) Total per year
British Gas £543 £577 £1,120
EDF Energy £669 £636 £1,305
E.ON £592 £612 £1,204
Npower £626 £627 £1,253
Scottish Power £629 £607 £1,236
SSE £595 £611 £1,206

Quotes gathered in July 2018. Source: Energy supplier websites.

The Big Six's Customer Service

With such huge numbers of customers, ensuring a consistently high standard of customer service is not easy for any supplier. Many customers stick with the Big Six names due to their familiarity and well-known brand name, but does this mean customers are actually satisfied with their customer service?

Looking at the Ofgem's research below, it's clear that none of the Big Six excel when it comes to customer care. Npower and Scottish Power customers appear to be the least happy with their supplier's service, bills and contacting the customer service team.

SSE on the other hand lead the big six in all three categories and have the highest percentage (35%) of customers that would recommend their supplier. Whilst they may offer the best service of the Big Six, only one in three customers would be happy to recommend SSE which is pretty poor overall.

  British Gas EDF Energy E.ON Npower Scottish Power SSE
Customers satisfied with service 71% 68% 71% 65% 68% 74%
Customers satisfied with understandable bills 73% 71% 74% 70% 70% 73%
Customers satisfied with contacting supplier 75% 68% 70% 65% 65% 75%
Customers that would recommend their supplier 35% 29% 33% 28% 28% 35%

Correct as of February 2018. Source: Ofgem.

Big Six Complaints

Between the Big Six, Scottish Power receive the most complants with around 2,800 complaints for every 100,000 customers. However, SSE and E.ON follow closely behind, both with around 2,500 complaints each per 100,000 customers. Interestingly, British Gas can boast the fewest complaints with just under 1,500 per 100,000 customers.

Npower is the supplier that takes the longest to resolve complaints - only solving aound half of customer complaints within one working day. Compare this to E.ON who manage to resolve a much better rate of 78% of complaints within a day.

  British Gas EDF Energy E.ON Npower Scottish Power SSE
Complaints per 100,000 accounts * 1,486 2,291 2,517 2,208 2,799 2,546
Complaints resolved within 1 day * 60% 58% 78% 49% 54% 77%

* Third quarter 2018 (July - September). Source: Ofgem.

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