Who are the big six energy providers?
The ‘big six’ is a term often used to describe the biggest energy companies operating in the UK – note, they don’t have to be British-owned to qualify for this list.
As of June 2025, the big six energy suppliers (in order of size) are:
Octopus Energy
It’s been a meteoric rise for Octopus since it first entered the UK energy market in 2016 thanks to a combination of natural growth and acquisitions. Octopus overtook British Gas in late 2023 to become the UK’s largest electricity supplier and has closed the gap in the gas market to make it the UK’s overall largest energy supplier as of June 2025. Find out more about the pro-renewables supplier here.
British Gas
Britain’s oldest energy supplier remains the UK’s largest gas supplier as of June 2025 and is its second-largest electricity supplier. Find out more about British Gas here.
E.ON Next
The UK’s third largest energy supplier as of June 2025 is E.ON Next. It secured this spot primarily thanks to its acquisition of npower’s customer base, which was completed in 2021. Read more about the German-owned company here.
OVO Energy
OVO Energy is the UK’s fourth-largest energy supplier, thanks largely to its acquisition of SSE’s 1.5 million customers in 2019. This British company was formed in 2009, and you can find out key information about its prices, tariffs and more here.
EDF Energy
The UK’s fifth-largest energy supplier is French-owned EDF, which has been a staple of the big six since 2002. The state-owned enterprise is best known for its nuclear power generation. Find out more about EDF here.
ScottishPower
As of June 2025, ScottishPower remains entrenched as the UK’s sixth largest energy supplier. Despite its name, the company is actually Spanish-owned. Find out more about ScottishPower here.
Has the big six always been the same?
No, there have been a few changes over the past decade or so. Traditionally, the big 6 energy suppliers were British Gas, EDF Energy, E.ON, npower, ScottishPower and SSE. At the height of their influence, these companies supplied seven out of 10 British households with gas and electricity.
However, smaller suppliers have started gaining a greater foothold in the UK. They're not only having an influence on the number of customers the big six supply, but they're also redefining what the big six are.
SSE's exit
In December 2019, SSE announced that it had reached an agreement with OVO for the latter company to acquire its customer portfolio.
npower's exit
In 2021, npower agreed a deal to move its customer base to E.ON, which shifted all of its customers to a new sub-brand called E.ON Next. This left British Gas, EDF Energy, E.ON Next, OVO and ScottishPower as five of the biggest suppliers in the country.
Shell Energy's exit
Meanwhile, First Utility, one of the more prominent challenger energy brands, was acquired by Shell and renamed Shell Energy. With the weight of one of the world's most recognisable and powerful companies behind it, Shell Energy emerged as a legitimate competitor to the current dominant suppliers. However, in the summer of 2023, Shell announced it would be selling its domestic energy business in the UK to Octopus and exiting the market. That process was completed on 1 December 2023.
Octopus continued to grow its customer base throughout 2024 through a combination of acquisitions and switching customers – the company claims nearly one million people switched to Octopus during that year.
As of June 2025, Octopus is the UK's largest energy supplier in terms of market share, supplying 24% of electricity customers and 24.1% of gas customers.
This means that, since the early 2000s, the energy market has undergone significant change in terms of which suppliers have dominated market share. The chart below demonstrates this (in terms of electricity suppliers) – look out for Octopus's rise right at the end of the timeline.
As of February 2025, we're back to a “big six” of energy companies in the UK based on market share, but one that looks very different to the one most people might think of.
What are the dangers of an energy market dominated by six UK energy companies?
The main issue with just six firms providing the vast majority of the UK with energy is the potential for this dominance to result in uncompetitive tariffs and high energy bills.
The UK’s economy is built on the principle of markets being competitive. The more companies exist in a certain sector, the more competition there will be. This competition then forces firms to offer customers the best possible deals. As of April 2025, there were 22 energy suppliers operating in the UK according to Ofgem.
Why don't more people switch energy providers?
Before the energy market crisis, there were many misconceptions about how hard it is to switch energy suppliers. For example, some people believed their cables and pipes required replacing or that, if they rented, they wouldn’t be allowed to change.
However, switching couldn't be easier or more accessible - when you switch your supply remains the same as before, delivered through the same infrastructure through your existing pipes and cables. The only difference is who charges you for that energy.
Should I switch to a small supplier?
Smaller energy suppliers represent a valid alternative to the bigger names. Small suppliers often offer deals on par with, or in some cases cheaper than, the big six, and can provide a more comprehensive level of customer service. However, many people remain unsure about making the switch, even if they could end up making a saving.
The main reason customers are afraid to move to a small supplier is that they fear that independent gas and electricity providers are more likely to go out of business. This isn't an unfounded fear, as there is very little to prevent anyone setting up an energy supply business, and many smaller companies have gone out of business over the past couple of years alone. However, it’s worth noting that you won’t be cut off if your supplier suddenly stops trading – Ofgem will step in to ensure your supply continues while it appoints you a new supplier.
Other concerns include customer service not matching up to that of the big six suppliers, or simply a lack of willingness to trust a brand they have never heard of.
How do I switch energy supplier?
Switching energy supplier is easy - all you need is your postcode and current energy provider and tariff and the process only takes a few minutes. Run an energy comparison by entering your postcode below.
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