Key Takeaways
The Big Four dominate the FTSE 250. PwC leads with 77 audit appointments, followed by EY (56), Deloitte (38) and KPMG (34). Together, they audit 205 of the index’s 250 companies.
Challenger firms are gaining ground. Seven non-Big Four firms account for 45 appointments, with BDO leading the group with 25.
Investment companies account for much of the challengers’ presence. Of the 45 non-Big Four appointments, 23 are in closed-end investment companies. BDO alone audits 15 of these businesses.
The Big Four remain entrenched across operating sectors. They audit 131 of the 151 companies outside the closed-end investment and REIT categories.
Audit appointments do not tell the whole story. Fees vary considerably between investment trusts and large operating businesses, meaning a firm’s share of appointments does not necessarily reflect its share of audit revenue.
The FTSE 250 is considerably more competitive than the FTSE 100. Challenger firms audit 45 FTSE 250 companies, compared with just four in the FTSE 100.
Jump to the full searchable table of all 250 FTSE 250 companies and their auditors
Britain’s FTSE 250 audit market is opening up to smaller firms. Over the past decade, challenger firms have significantly increased their presence among the country’s mid-sized listed companies, with BDO emerging as the strongest competitor to the Big Four.
But how far has that competition really extended?
Big4News examined the auditors of all 250 companies in the FTSE 250, using the index composition effective from 21 September 2026. The findings reveal an important distinction: while firms outside the Big Four have established a meaningful presence, a substantial part of that presence is concentrated in investment companies.
Among the FTSE 250’s commercial and other businesses, PwC, EY, Deloitte and KPMG remain firmly entrenched.
PwC leads the FTSE 250 audit market
PwC has the largest number of audit appointments in the September 2026 dataset, auditing 77 companies. EY follows with 56, Deloitte with 38 and KPMG with 34.
Together, the four firms account for 205 of the 250 audit appointments.
BDO is the largest challenger, auditing 25 companies. Grant Thornton and RSM each audit six, followed by Forvis Mazars with four, Johnston Carmichael with two, and Crowe and MHA with one each.
Altogether, 11 audit firms are represented in the index.
The figures confirm the Big Four’s continuing dominance, but also show that the market is no longer their exclusive preserve. BDO, in particular, has established a substantial portfolio of listed-company audits.
In 2016 mid-sized firms audited 9 FTSE 250 clients. This has now grown to 43.
BDO’s portfolio grew from 2 to 24 companies over the same period.
Investment companies account for much of the challengers’ presence
A closer examination of the sectors audited by challenger firms reveals a striking concentration.
The FTSE 250 contains 86 companies classified as closed-end investments, including investment trusts specialising in equities, private equity, infrastructure and other assets. Unlike operating businesses, these companies primarily invest in portfolios of assets rather than produce goods or provide services.
Non-Big Four firms audit 23 of these companies, accounting for more than half of their 45 FTSE 250 audit appointments. They also audit two of the index’s 13 real estate investment trusts (REITs).
BDO alone audits 15 closed-end investment companies, making this the largest segment of its FTSE 250 portfolio. However, its reach extends into other sectors. Its clients include Galliford Try in construction, Mitie in industrial support services, Halfords in retail, Playtech in travel and leisure, and Ceres Power in alternative energy. BDO also audits Applied Nutrition, XPS Pensions and Foresight Group, alongside property businesses Workspace Group and Supermarket Income REIT.
Other challengers have smaller and more varied portfolios.
Forvis Mazars audits four FTSE 250 companies, three of them closed-end investments. Johnston Carmichael’s two appointments are also both in this category.
Grant Thornton combines investment-company audits with appointments in travel and leisure, industrial support services and technology hardware. RSM audits six companies spanning software and computer services, retail, general industrials, consumer businesses and closed-end investments.
Crowe and MHA each have one FTSE 250 appointment, in media and food production respectively.
The concentration of challenger appointments among investment companies may reflect differences in audit requirements. Although investment-company audits can involve complex valuations, financial instruments and specialist assets, they do not necessarily require the same operational audit capabilities as multinational businesses involved in manufacturing, retail or international trading.
These differences may help explain why challenger firms have established a stronger presence in this sector than in much of the wider FTSE 250.
The Big Four remain entrenched across operating industries
The sectoral distribution of Big Four appointments helps explain the continued concentration.
PwC leads the overall rankings and has a particularly broad portfolio.
It audits 22 closed-end investment companies, eight businesses classified as investment banking and brokerage services, and companies across sectors including pharmaceuticals, industrial transportation, construction and retail.
EY audits 25 closed-end investment companies — more than any other firm — alongside companies in software and computer services, industrial support services, construction and real estate.
Deloitte’s appointments are spread across a variety of sectors, including electronic and electrical equipment, industrial support services, real estate investment trusts and telecommunications.
KPMG has a different concentration of appointments. Its portfolio includes companies in retail, travel and leisure, aerospace and defence, as well as financial services and investment companies.
These differences illustrate that the Big Four are not interchangeable in their FTSE 250 client portfolios.
PwC and EY have particularly substantial investment-company practices. Deloitte has a more dispersed selection of industrial and service-sector appointments, while KPMG has a notable presence in selected consumer and aerospace businesses.
At the same time, the Big Four collectively audit every FTSE 250 bank in the dataset, all four pharmaceuticals and biotechnology companies, and all seven electronic and electrical equipment companies.
These sectoral examples are consistent with the continuing importance of the Big Four among companies requiring extensive operational, international or specialist audit capabilities.
Audit appointments tell only part of the story
The number of companies audited by each firm does not necessarily reflect the economic value of those appointments.
Audit fees vary substantially across the FTSE 250, reflecting differences in company size, international operations, business complexity and the scope of audit work required.
The distinction is particularly relevant to investment companies, where challenger firms have established their strongest presence. Some investment trusts pay relatively modest audit fees compared with multinational operating businesses, although fees vary considerably depending on the size and complexity of their portfolios.
For example, the latest audit fee recorded for Allianz Technology Trust, audited by Forvis Mazars, is £51,000, while Aberforth Smaller Companies Trust, audited by Johnston Carmichael, reports £38,000.
By contrast, several large operating businesses pay millions of pounds annually for their audits. WPP’s reported £47 million fee includes an internal-controls audit component, while Serco’s audit fee is £6.6 million and Mondi’s is approximately £6.37 million.
BDO’s portfolio also includes substantial engagements. The recorded audit fees for Mitie and Playtech are approximately £5.29 million and £4.80 million respectively, demonstrating that the firm’s presence extends beyond smaller investment-company audits.
These differences help explain why market share measured by audit appointments may present a different picture from market share measured by audit fees.
The Big4News dataset does not support a complete like-for-like comparison of audit-fee market shares. Current-auditor fees remain unavailable for 13 companies, while differences in reporting periods, audit scope and fee attribution introduce further limitations.
Nevertheless, the individual disclosures illustrate an important point: greater competition in the number of listed-company audit appointments does not necessarily translate into an equivalent redistribution of audit revenue.
How does the FTSE 250 compare with the FTSE 100?
The difference between Britain’s two leading stock-market indices is striking.
In the FTSE 100, the Big Four audit 96 of the 100 companies, leaving just four appointments to challenger firms. BDO audits two companies, while Grant Thornton and Forvis Mazars audit one each.
The FTSE 250 presents a more competitive picture. The Big Four audit 205 of its 250 companies, leaving 45 appointments to seven challenger firms.
The identity of the leading auditor also changes. Deloitte ranks first in the FTSE 100 with 27 appointments, followed closely by PwC with 25 and KPMG with 24. In the FTSE 250, PwC leads comfortably with 77 appointments, ahead of EY with 56.
BDO’s position illustrates the difference between the two markets. It audits just two FTSE 100 companies but has established a portfolio of 25 in the FTSE 250.
The comparison suggests that challenger firms have made considerably greater progress among Britain’s mid-sized listed companies than among its largest businesses.
The FTSE 250 may therefore be providing a route for smaller firms to expand their listed-company audit practices, but that has yet to translate into comparable competition at the top of Britain’s corporate market.
About the Data
This analysis is based on Big4News research into the 250 companies comprising the FTSE 250 as at 21 September 2026.
The index contains 251 security lines, but Seraphim Space Investment Trust’s ordinary and C share classes are counted as one company, resulting in 250 company records.
For each company, Big4News identified the principal statutory auditor, the first financial year audited by that firm where reliably established, and the latest available audit fee. Information was drawn primarily from company annual reports, audit disclosures and regulatory filings.
Audit appointments are attributed to the relevant audit firm, with predecessor firms and changes in legal entities treated in accordance with the research methodology. Each company is counted once in the appointment analysis.
Audit fees are presented in pounds sterling and relate to the latest available reporting periods, which vary between companies. Where necessary, foreign-currency amounts were converted using documented exchange rates.
Historical auditor start dates could not be reliably established for 15 companies, while current-auditor fees were unavailable for 13. These fields have been left blank rather than estimated. Individual company notes identify material qualifications and disclosure limitations.
The sectoral analysis uses the classifications recorded in the research dataset. Closed-end investments and real estate investment trusts are distinguished from other sectors to examine differences in auditor representation.
For further information on sources, definitions and research procedures, see Who Audits? Sources and Methodology.
Explore the Full FTSE 250 Dataset
The searchable table below identifies the auditors of all 250 companies, including auditor tenure, audit fees and relevant qualifications.
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About the author: Claudine Cassar is the founder and editor of Big4News, covering audit, consulting, regulation and governance across Deloitte, PwC, EY and KPMG.