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A guide to the Big Six energy suppliers

The ‘Big Six’ are the largest energy suppliers in the UK. Find out a bit more about them and see if bigger means better when it comes to choosing where your energy comes from.

The ‘Big Six’ are the largest energy suppliers in the UK. Find out a bit more about them and see if bigger means better when it comes to choosing where your energy comes from.

Written by
Dan Tremain
Energy and business energy expert
Last Updated
11 JANUARY 2024
6 min read
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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 at the end of 2022.

Energy regulator Ofgem’s definition of a large energy company is one that has more than a 5% market share. But since energy companies were privatised, the make-up of the Big Six has changed.

You can see the changes from 2004 to 2022 in our table:

The Big Six energy companies’ market share

Company Market share
Q1 2004
Company Market share
Q4 2022
  Electricity Gas   Electricity Gas
British Gas 24% 55.8% British Gas 20.4% 28.2%
E.ON 21% 12.4% E.ON 17.3% 14.5%
npower 15% 9.2% Ovo 13.3% 11.2%
SSE 14% 10.1% EDF 11.4% 9.5%
EDF 14% 4.6% Octopus 11.2% 11.5%
Scottish Power 11% 8.6% Scottish Power 9.2% 7.8%

Source: Ofgem

SSE disappeared from the Big Six after it reached an agreement in 2019 for OVO to acquire its customers. And npower completed a deal with E.ON in 2021, under which its customers were moved onto E.ON’s 100% renewable electricity brand E.ON Next.

Collectively, the Big Six supply gas or electricity to approximately 71% of energy bill payers in the UK.

But as more independent suppliers vie for a share of the market, the dominance of these major players is under threat.

Shell Energy

You may sometimes hear references to the Big Seven – with Shell Energy, which has a 4.5% market share, as the seventh player.

But things are set to change again as Shell Energy has announced that it’s up for sale. This move won’t affect business energy customers, and households will be moved over to a new company when the buyer is confirmed.

The sale could bring a smaller company above the 5% mark or move one of the other players up the table. It looks likely that it will be one of the Big Six that acquires Shell Energy. Any sale would need to be approved by regulators before going ahead.

Your guide to the Big Six energy suppliers

Here are the Big Six UK energy suppliers by size.

British Gas

Aiming to be net zero greenhouse gas emissions by 2045

British Gas is the UK’s largest energy provider. It supplied gas and electricity to more than 7.5 million customers in 2021, 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.

E.ON

Aims to be net zero by 2050

Previously known as Powergen, E.ON powers about 5.6 million customers in the UK. It has a strong focus on innovative technologies. In fact, all its customers’ homes are powered with 100% renewable electricity. 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. 

Ovo

Aiming to be a zero carbon company by 2035

Launched in 2009, Ovo aims to plant one million trees a year. Customers on its Power Move plan get rewarded for using energy at greener and cheaper times of the day.

SSE sold its retail arm to Ovo Energy 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.

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 3.6 million homes and businesses. It’s the UK subsidiary of French energy company EDF Group (Electricité de France).

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 5 million+ homes and businesses.

After Bulb, which had a 5.5% market share, became insolvent in November 2021, it was acquired by Octopus. And in April 2023, M&S Energy customers also moved to Octopus, along with failed company Avro’s customers.

Scottish Power

Aiming for net-zero greenhouse gas emissions by 2039

Scottish Power provides energy to around 5 million homes and businesses in the UK. It’s now owned by Spanish energy firm Iberdrola and generates 100% of its electricity from its own wind farms.

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 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 when this is possible again.

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

The Big Six haven’t always been 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.

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. In the run-up to the energy crisis, more customers seemed to switch away from the Big Six rather than to them.

But as wholesale energy prices increased, a number of smaller suppliers went out of business and their customers were moved to Big Six providers. Their size and resources can make them more stable.

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. 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, many of which have much higher levels of customer satisfaction than the Big Six, as you’ll see if you compare with us when possible again.

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

Smaller energy suppliers in 2023 include:

  • Ecotricity
  • Good Energy
  • 100Green
  • So Energy
  • Utility Point

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?

Switching (when available) can help keep prices competitive between suppliers as they fight to keep customers.

In the past, people have switched to tariffs offering better value for money or better customer service. Fixed tariffs can offer the benefit of knowing what your unit rate will be the same for a set period, which can help with household budgeting. They can also help protect you when prices are rising, but won't benefit from the advantage of cheaper prices if they fall.

Switching energy supplier 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?

A good way to switch energy providers is to compare what you would pay from different suppliers and their different tariffs based on your energy usage. Compare today to see if you could find a better deal.

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