Key Takeaways
The Big Four audit 96 FTSE 100 companies. Deloitte leads with 27 appointments, followed by PwC (25), KPMG (24) and EY (20).
Only three challenger firms are represented. BDO audits two companies, while Forvis Mazars and Grant Thornton audit one each.
The challengers’ clients are diverse. They include an investment trust, a mining company, an aerospace and defence group, and a technology services business.
The Big Four have different sectoral portfolios. PwC is particularly prominent in banking and investment services, while the other firms have different concentrations across insurance, energy, industrial and consumer businesses.
Audit fees vary enormously. Major international banking groups report fees running into tens of millions of pounds, while some investment companies pay less than £100,000.
The FTSE 250 is considerably more competitive. Seven challenger firms audit 45 companies in the mid-cap index, compared with just four challenger appointments in the FTSE 100.
The dataset reflects the index composition effective from 21 September 2026 and was most recently reviewed on 18 October 2026.
Jump to the full searchable table of all 100 FTSE 100 companies and their auditors
Britain’s largest listed companies have remarkably little diversity in their choice of external auditors.
Despite years of regulatory scrutiny, market reform proposals and efforts to strengthen smaller audit firms, PwC, Deloitte, EY and KPMG continue to dominate the FTSE 100.
Big4News examined the auditors of all 100 companies in the index, using its composition effective from 21 September 2026. The research identifies the principal statutory auditor, the first audited financial year where reliably established, and the latest available audit fee.
The findings reveal a highly concentrated market, but also significant differences between the Big Four’s individual client portfolios.
And the few exceptions to their dominance are particularly revealing.
Deloitte leads, but the Big Four are closely matched
Deloitte has the largest FTSE 100 audit portfolio, with 27 appointments.
PwC follows with 25, KPMG with 24 and EY with 20.
The remaining four appointments are divided between BDO, Forvis Mazars and Grant Thornton.
Unlike some other leading stock-market indices, no single firm has an overwhelming lead in the FTSE 100.
Deloitte, PwC and KPMG are particularly closely matched. EY has a somewhat smaller portfolio, but remains far ahead of every challenger.
Just four companies use auditors outside the Big Four
Only four FTSE 100 companies in the September 2026 dataset are audited by challenger firms.
BDO audits Alliance Witan, an investment trust, and Endeavour Mining, an international gold-mining business.
Forvis Mazars audits Babcock International, which operates in aerospace and defence, while Grant Thornton audits Computacenter, an international technology services company.
Nevertheless, four appointments among 100 companies remain a very small foothold.
The Big Four have different sectoral strengths
The overall ranking conceals important differences in the industries audited by each firm.
PwC has a particularly strong presence in financial services. It audits three of the FTSE 100’s seven banks and three of the seven companies classified as investment banking and brokerage services.
Its wider portfolio includes companies in beverages, aerospace and defence, utilities, industrial support services and real estate.
KPMG has a different mix of appointments, including pharmaceuticals and biotechnology, life insurance, investment trusts, software and computer services, and travel and leisure.
Deloitte’s portfolio is spread across a broad range of industries. It audits companies in energy, mining, utilities, retail, industrial support services and banking, among others.
EY’s clients include life and non-life insurers, investment banking and brokerage businesses, as well as companies in mining, consumer products, telecommunications and other industries.
The patterns are revealing, although individual sector counts are relatively small.
PwC has the largest number of banking appointments, while KPMG has a particularly visible presence in pharmaceuticals and insurance.
Deloitte’s overall lead is not based on dominance of any single sector. Its portfolio is distributed across several major parts of the British economy.
Audit fees tell a different story
Audit appointments measure the number of companies audited, not the economic value of those relationships.
The FTSE 100 dataset reveals substantial differences in audit remuneration.
HSBC, audited by PwC, records approximately £80.9 million in audit fees.
Barclays, audited by KPMG, reports £70 million.
Other major international businesses also report substantial fees, including BP, audited by Deloitte, and Shell, audited by EY, both with recorded amounts exceeding £40 million.
These disclosures reflect the substantial scale and complexity of international group audits, which may involve numerous subsidiaries, business lines, jurisdictions and regulatory requirements.
At the other end of the spectrum, Alliance Witan, audited by BDO, has a recorded audit fee of £89,000.
Auditor relationships are not as permanent as they once were
The FTSE 100 dataset also provides insight into the duration of audit relationships.
Some relationships extend back many years. The earliest first-audit year recorded in the dataset is 2003, for PwC at Coca-Cola HBC. Other long-standing relationships include Deloitte at Barratt Redrow and EY at Fresnillo, both recorded from 2008, and PwC at St. James’s Place from 2009.
These start years are drawn from company disclosures and reflect the research methodology. The applicable auditor-rotation requirements may differ according to an issuer’s jurisdiction and regulatory status.
By contrast, more recent appointments include Forvis Mazars at Babcock International and Grant Thornton at Computacenter.
Britain’s regulatory framework places limits on how long public-interest entities can retain the same statutory audit firm. Mandatory tendering and firm-rotation requirements are intended to prevent indefinitely continuing audit relationships and create opportunities for competition.
Yet rotation does not necessarily broaden the field of firms capable of winning the appointment.
A company replacing one Big Four auditor may simply appoint another.
The resulting market can therefore experience regular auditor changes while remaining highly concentrated among the same four firms.
How does the FTSE 100 compare with the FTSE 250?
The contrast with Britain’s second-tier index is striking.
In the FTSE 100, the Big Four audit 96 companies, leaving just four appointments to three challenger firms.
In the FTSE 250, the Big Four audit 205 of the 250 companies, while seven challengers account for the remaining 45 appointments.
BDO illustrates the difference particularly clearly. It audits two FTSE 100 companies but 25 in the FTSE 250.
The identity of the leading auditor also changes. Deloitte ranks first in the FTSE 100, while PwC leads the FTSE 250.
But the comparison requires an important qualification.
Big4News’s FTSE 250 sectoral research found that 23 of its 45 challenger appointments are concentrated in closed-end investment companies.
The larger number of challenger appointments in the FTSE 250 therefore does not necessarily indicate equally strong competition across all types of business.
Even so, the difference between the two indices is substantial.
The FTSE 250 offers challenger firms a considerably greater presence in Britain’s listed-company audit market. In the FTSE 100, the four largest firms remain almost unchallenged.
About the Data
This analysis is based on Big4News research into the FTSE 100 companies comprising the index as at 21 September 2026.
The constituent roster was reconciled against FTSE Russell’s official constituent information and September 2026 review changes.
For each company, the dataset identifies its principal statutory auditor, the first financial year audited by that firm and the latest available audit-fee disclosure.
The first-audit year refers to the audit-firm relationship, not the appointment of an individual engagement partner. Predecessor relationships and legal-entity changes are treated according to the published research methodology.
Audit fees are presented in pounds sterling. Foreign-currency disclosures have been converted using documented exchange rates where applicable.
Some fee amounts are subject to qualifications concerning audit scope, reporting periods, fee attribution and predecessor auditors. These are explained in the research record and relevant company notes.
The dataset was reviewed on 18 October 2026, with its constituent and auditor snapshot dated 21 September 2026.
For details of the research procedures, definitions and disclosure standards, see Who Audits? Sources and Methodology.
Explore the Full FTSE 100 Dataset
The searchable table below identifies the external auditor, first audited financial year, audit fee and relevant qualifications for all 100 companies.
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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.