Market shares of Big Six domestic electricity suppliers in Great Britain 2010-2021

British Gas is the largest retail electricity supplier in Great Britain. Despite a notable decline throughout the years, it still accounted for 18 percent of the market in the first two quarters of 2021. E.ON followed closely, with a market share of 17 percent during the same period.

 Changes in the Big Six 

  The electricity market in Great Britain has historically been controlled by a few providers, collectively known as the Big Six . These include British Gas, E.ON, SSE, EDF, npower, and Scottish Power. However, in recent years, there have been significant changes in their composition. In January 2020, OVO Energy acquired SSE's electricity and gas distribution business, albeit continuing to sell energy under the SSE brand. Meanwhile, npower was acquired by E.ON in 2019, turning the Big Six into a de-facto Big Five. The npower brand is expected to be slowly discontinued.

 Growing competition in the British electricity supply market 

In 2010, the Big Six held 100 percent of the domestic electricity supply market in Great Britain. In order to promote a more competitive market, the British energy regulator, Ofgem, enacted a series of market reforms aimed at increasing access for smaller players. The past decade has seen a significant number of customers switching from large electricity suppliers to small and mid-tier suppliers, causing the Big Six’s market share to dip below 70 percent in 2021.