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The Big Six Energy Suppliers

Known collectively as the 'Big Six', these were the biggest legacy suppliers of gas and energy in the UK. The Big Six are:

  • British Gas
  • E.ON
  • EDF Energy
  • SSE Energy
  • Scottish Power
  • nPower

Although the hold the biggest market share, they are by no means the only energy suppliers available. In recent years, newer suppliers such as Octopus and OVO Energy have emerged, threatening the oligopolistic control once held by the Big Six.

About the Big Six

The introduction of the Gas Act in 1986 and Electricity Act in 1989, created the framework for the privatisation of the UK's energy and gas supply.

Heading into the 90s, further privatisation, as well as acquisitions and mergers, eventually led to the creation of the six major energy and gas suppliers we have today.

As of Q1 2022, the Big Six have a combined market share of 72% for both electricity and gas supply in the UK.

The withdrawal of the Big Six category

In November 2020, energy regulator Ofgem announced that due to the emergence of numerous competitors in the market, as well as an increasing number of acquisitions making it harder to identify and define the Big Six, that the 'Big Six' category would be dissolved and relabelled as 'Large'.

Under the new classification system, all energy suppliers with 5% or more market share are now classed as a ‘Large’ supplier, with those holding less than 5% market share falling into 'Medium' and 'Small' categories, respectively.

British Gas

With a history spanning more than 200 years, British Gas is the oldest and largest energy supplier in the UK.

Although its overall market share has reduced over the years, it has seen a recent uptick thanks to its absorption of Together Energy's customers after they went bust in January 2022.

British Gas currently has a combined total of more than 10 million gas and electricity customers.

EDF Energy

`Formed in 2002 following the acquisition and merger of a number of British energy companies. Today EDF is owned by Electricité de France, itself 85% owned by the French government.


Originally known as Powergen and one of the first suppliers to emerge after the 1989 Energy Act. Powergen changed its name to E.ON after it was purchased in 2002 by German energy company, E.ON AG.


Formerly known as Innogy plc, nPower has been a subsidiary of E.ON since January 2019.


Established in 1998, SSE was borne from a merger of Scottish Hydro-Electric and Southern Electric, with its full name being Southern and Scottish Energy.

In January 2020, OVO Energy - a rival company founded in 2009 - purchased the retail arm of SSE's business. The purchase of SSE by OVO heralded the end of the original Big Six.

Scottish Power

Founded in 1990 and privatised a year later, Scottish Power has been a mainstay of the UK energy market. The company was purchased by Spanish utility firm Iberdrola in 2006, but continues to be based out of Glasgow.

Despite its name, Scottish Power supplies gas and electricity to more than 5 million homes and businesses across the UK.

The rise of Octopus Energy

Although not a part of the traditional Big Six, Octopus Energy - established in 2015 - is now the fourth largest energy supplier in the UK, with more than 3 million domestic and business customers.

Should you switch from the Big Six?

Although complaints relating to poor customer service and steep prices are far from uncommon for the Big Six, many seem reluctant to switch away.

Much of this reluctance comes from a fear that switching to a smaller supplier might incur a level of risk. For example, from July 2021 to March 2022, the wholesale market price suppliers paid for gas and electricity rose to unprecedented levels. As a result, 29 energy suppliers went into receivership, affecting nearly four million households.

However, Ofgem operates a safety net - the 'Supplier of Last Resort' (SoLR) - to protect consumers should their energy supplier go bust.

Ofgem uses the Supplier of Last Resort process to appoint an alternative supplier who will then absorb the customers of the energy company that failed. This procedure ensures customers can continue on as normal, with no disruption to their gas and electricity supply.

Why should I switch energy supplier?

If no-one switched suppliers, there would be no need for energy companies to lower prices and compete for customers. In other words, switching is a key component to ensuring that energy markets are accountable to their customers.

Switching is also an easy step you can take to make sure you've got the best energy deal possible.

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