Who Audits Public Companies – United Kingdom 2020

This post is a part of Audit Analytics’ series on audit market concentration across select countries in Europe.

Overall, the Big Four firms retained 84.3% of the market share for the major UK indices in 2020, a slight decline from the 88% market concentration seen in 2019.1 While PwC signed opinions for 27.5% of major LSE index-listed firms, the rest of the Big Four dropped to 56.8% of the market. Relative to 2019, this drop represents a slight decline for KPMG and Deloitte and a slight increase for EY.

Outside the Big Four, BDO saw the greatest gains in 2020, up to 7.9% from 5.6% in 2019. Grant Thornton audited 4% of public companies on UK indices. The remainder were audited by eight firms, with a less than 1% market share held by each.

Who Audits United Kingdom

FTSE 100

Although no new firms broke into the market for the FTSE 100 as of 2020, the distribution of auditors narrowed to become nearly even amongst the Big Four. As anticipated in our last report, KPMG took the lead on audits of the FTSE 100. While KPMG’s share of the market remained unchanged at 28%, PwC’s share dropped 4%, leaving them with a 25% share overall and the second-largest share of the market. EY showed the greatest change, jumping 5% to secure a 24% share of the market, and Deloitte dipped to 23%.

2021 may portend greater shifts in the make-up of the audit market for this index. In recent weeks, Darktrace plc has made the shift from the FTSE 250 to the FTSE 100. While they were still a constituent of the FTSE 250 as of the publication of their Annual Report in September (and their 2021 IPO places them beyond the scope of this report), they continue to retain Grant Thornton as their signing auditor.

FTSE 250

PwC expanded its share of the market to lead with audits of 32% of the FTSE 250. While KPMG’s share dropped to 21%, Deloitte’s declined to 20%, allowing KPMG to just edge out Deloitte for the second greatest market share. EY signed opinions for 18% of FTSE 250 companies in 2020, rounding out the Big Four’s share of the market at 91%.

While there were few changes in the composition of the market overall, 2020 saw the share for non-Big Four firms nearly double, collectively increasing by 5% from their 2019 share of the market. The main source was a 4% increase by BDO to a 6% total share of FTSE 250 audits. Grant Thornton and MHA MacIntyre Hudson’s shares both either stayed constant or slightly increased. RSM is a new entrant to this market, taking over from Grant Thornton after an extended search by Frasers Group Plc (formerly known as Sports Direct International) and bringing the non-Big Four market share to 9% total.


Consisting of the 50 largest firms on the LSE’s AIM, the audit market for the FTSE AIM UK 50 showed some fluctuation. While Big Four firms account for 66% of this market, BDO jumped to hold the same share as PwC in 2020. Each audited ten companies and collectively accounted for a 40% market share at the top of the ranking. They were followed by KPMG and EY, each auditing eight companies for a combined market share of 32%, and Deloitte, with seven audits and 14% of the market share. Grant Thornton audited five companies, up by one from 2019, and held a 10% share of the market. RSM and Jeffreys Henry maintained their market share from 2019.


As it encompasses companies on the FTSE AIM UK 50 as well as the 50 next-largest AIM companies, the FTSE AIM 100 showed similar movements in the audit market relative to 2019. PwC maintained its share of 23%, while BDO displaced KPMG with a market share of 15% to take the next-highest share. KPMG dropped slightly to a 14% market share, while EY, Grant Thornton, and Deloitte trailed at 13%, 12%, and 11%, respectively. PKF Littlejohn and the Nexia network each held a 3% market share, and RSM, 2%. All other firms held a 1% market share.

1. This analysis covers Audit Analytics’ current constituent list of four major indices tracked by the London Stock Exchange – for the Main Market, the FTSE 100 and the FTSE 250; and for the AIM, the FTSE AIM UK 50 and the FTSE AIM 100.

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