A guide to the Big Six energy suppliers

Who are the Big Six energy suppliers?

Historically, the ‘Big Six’ is the collective name given to the six top energy suppliers in the UK. There were 22 active suppliers of energy in the UK in the last quarter (Q4) of 2024.

For a long time, the ‘Big Six’ energy suppliers were British Gas, EDF, E.ON, npower, Scottish Power and SSE. However, in December 2019, this began to change when SSE announced that OVO was to acquire its customer portfolio. Then in 2021, npower agreed to move its customer base to E.ON. And then to further shake things up Shell, an up-and-coming competitor to the 'Big Six', announced in the summer of 2023 that it would be selling its domestic energy business – despite acquiring First Utility in 2018 – to Octopus and thus exiting the market. This deal was completed in December 2023 and has seen former underdog Octopus propel through the ranks and (at the time of writing) surpass British Gas.

Energy regulator Ofgem’s definition of a large energy company is one that has more than a 5% market share.

In Q4 2024, the combined market share of the large legacy suppliers was 67% for both electricity and gas, leaving them still dominant. Other newer large, medium and small suppliers accounted for the remaining share in both fuels.

You can see the changes from 2004 to 2024 in our table:

The Big Six energy companies’ market share

Source: Ofgem

Big Six in Northern Ireland

Northern Ireland has its own Big Six:

• Budget Energy

• Click Energy

• Electric Ireland

• Power NI

• SSE Airtricity

• Share Energy.

But in May 2024 Dublin-based Electric Ireland said it would be pulling out of Northern Ireland with its customers having to find a new supplier at some point. On the other hand, new supplier Share Energy has entered the market promising a profit-sharing arrangement with its customers – when it becomes profitable.

Your guide to Britain's Big Six energy suppliers

Here are the Big Six UK energy suppliers by size:

British Gas

Aiming to be a net-zero business by 2045 (40% greenhouse gas reduction by the end of 2034)

British Gas is the UK’s largest energy provider. It claims to be the world’s first utility company, set up in 1815, so more than 200 years old. It supplied gas and electricity to more than 7.53 million residential customers in 2024, with a wide range of tariffs available. It’s owned by parent company Centrica. British Gas took on a number of customers from failed energy suppliers in recent years, including Together Energy and Bristol Energy.

The British Gas Energy Trust support fund has helped more than 21,000 British Gas customers since 2021 with energy debt write-off grants worth up to £2,000. British Gas also offers help to non-customers, too.

British Gas offers fixed, variable and EV tariffs, plus a special tariff for homes with Dimplex Quantum storage heaters as of April 2025, but this may be subject to future change.

E.ON Next

Aims to achieve climate-neutrality in its own operations by 2040 and to help achieve the UK’s target of net zero carbon emissions by 2050

E.ON powers about 5.6 million customers in the UK. It has a strong focus on green and innovative technologies and offers tariffs backed by 100% renewable sources including its tariff powered by Yorkshire wind farms with Next Gust. The German-owned company says it has invested £3.5 billion in renewables since 2009. E.ON also took control of npower in early 2019.

E.ON offers fixed, tracker, variable, EV and green tariffs as of April 2025, but this may be subject to future change.

OVO

Aiming to be a zero carbon company by 2035

Launched in 2009, OVO’s Plan Zero commitment to reach net zero by 2035 is a combination of cutting its carbon emissions by 90% and only offsetting 10% of emissions it can’t avoid or reduce. To further its green credentials OVO aims to plant one million trees a year. Customers on its Power Move plan are rewarded for using energy at greener and cheaper times of the day if they meet certain targets.

OVO Energy took over SSE’s retail arm to in January 2020, with 3.5 million customers moving as a result. The takeover means that OVO now supplies energy to around 5 million customers in the UK.

OVO offers variable, fixed, EV, and greener tariffs together with a tariff that included boiler cover and one with smart thermostats as of April 2025. But this may be subject to future change.

EDF Energy

Aims to achieve net zero by 2050

Britain’s biggest generator of zero-carbon electricity – from wind, nuclear and solar – provides energy to more than 3.7 million homes and businesses. It’s the UK subsidiary of French energy company EDF Group (Electricité de France).

EDF, from time to time, sets challenges to its customers to help them save electricity or shift their electricity usage away from peak times. To encourage behavioural change, it sometimes offers rewards such as free hours of electricity.

EDF offers fixed, variable, tracker and EV tariffs. It also has tariffs for homes with heat pumps or solar and batteries, with some tariffs requiring a smart meter. These tariff types were in place as of April 2025, but this may be subject to future change.

Octopus

Aims to reach net zero by 2030

Launched in 2016, Octopus claims to be 100% green, with all its energy coming from renewable sources such as wind, sun and water. It powers 6 million+ homes and businesses.

Octopus has grown rapidly, taking over customers from other suppliers such as Bulb, which had around 1.5 million customers , when it became insolvent in November 2021. And in April 2023, M&S Energy customers also moved to Octopus, along with failed company Avro’s customers. Then in December 2023, Shell Energy customers also moved over to Octopus when Shell decided to exit the domestic energy market.

With the aim of helping vulnerable customers keep bills down during the cost-of-living crisis, Octopus set up a scheme to keep the person warm rather than the room. It gave away 7,000 free electric blankets to customers who needed them most.

Octopus offers a range of smart tariffs including ones for people with heat pumps, solar or EVs and a tracker tariff as well as fixed and standard tariffs. Octopus offered these types of tariffs in April 2025, but these may be subject to future change.

Scottish Power

Aiming for net-zero greenhouse gas emissions by 2039

Scottish Power provides energy to more than four million domestic customers and businesses in the UK. It’s now owned by Spanish energy firm Iberdrola and for its renewable tariff generates 100% of its electricity from its own wind farms. It also offers boiler care plans.

Unusually for energy companies, Scottish Power is transparent about the number of complaints it receives and how quickly these are resolved, indicating its intentions around customer service. It also promises that if it launches a better tariff, you can move at any time with no exit fees.

It offers a Heat Pump Saver tariff and a SmartGen+ tariff for homes with solar panels, alongside green, variable, fixed tariffs and capped.

Who is the cheapest of the Big Six energy suppliers?

No one supplier is the cheapest all-round. It will depend on the tariff you choose, where you live, how you use energy and how you’re billed.

What you pay also varies from region to region, both for your energy unit price and standing charge.

The best way to find out which company is offering the cheapest deal is to compare prices.

Is it a good idea to stick with one of the Big Six?

Which provider you choose is all down to personal preference, cost, the type of tariff you are looking for and customer service.

The Big Six aren't necessarily the cheapest option when comparing energy prices, although bigger companies can sometimes afford to be more competitive with their pricing.

Energy is energy. Regardless of who you buy it from, it will come to your pipes and switches the same way. Which provider you choose is all down to personal preference, cost and customer service.

Some will also have special deals for particular tariffs such as for charging EVs or using heat pumps or solar power. And the Big Six providers all participate in the Warm Home Discount scheme, but not all smaller ones do. See the suppliers who are part of the scheme.

The Big Six are big because they have the most customers – but much of this is due to how long they’ve been around for, or which companies they’ve merged with, rather than because they deliver the best service and prices.

So you need to think about what matters most to you if you decide to switch.

How do I find an alternative to the Big Six?

If you don’t want to go with one of the Big Six, there are other options that you can compare. In the past, alternatives to the main UK energy suppliers have been relatively small-scale rivals. But with other disrupters that survived the energy crisis providing a different way of doing things, energy customers are being given real food for thought.

There’s also a raft of less-established companies to choose from. Some also have much higher levels of customer satisfaction than the Big Six, as you’ll see if you compare with us.

Smaller energy suppliers in 2025 include:

• Utility Warehouse

• Utilita

• So Energy

• Good Energy

• Ecotricity

• Fuse Energy (for electricity)

• Outfox the Market

• 100Green.

Some providers are dedicated to sustainable sourcing and green energy. So if you’re looking for an eco-friendly supplier, there are plenty of options.

Why should I switch energy supplier?

You may want to switch to get:

• A cheaper tariff

• Better customer service

• A different type of tariff – an EV tariff, for example.

Switching is easy these days with Ofgem’s switch guarantee. You won’t lose any energy supply and the switch should be completed within five working days. All you have to do is sign up to a new energy provider and they’ll do the rest.

How do I switch energy providers?

Start by comparing deals from different suppliers. When you compare with us, we’ll show you a range of deals based on your energy usage. Once you’ve decided to switch you can click through to the supplier’s website. You’ll need to provide them with information from your energy bill. They’ll then tell you when your supply will be switched. See our full guide to switching energy supplier.