PwC Beats BDO in Ranking of Auditors for UK-Listed Companies

PwC overtook its audit firm rival BDO to count the largest number of UK-listed companies as clients despite a shrinking market, a new ranking shows.

BDO had been the UK’s largest auditor by number of publicly traded clients since late 2020, but PwC took the top spot in the most recent quarter of this year, according to Adviser Rankings Ltd. The researcher tracks the market for audit firms hired to vet corporate financial accounting.

PwC is also the top-ranking UK auditor measured by the market valuation of its corporate clients, which totaled £1.3 trillion ($1.8 trillion) in May, the research found. KPMG, Ernst & Young, and Deloitte took the next three slots, while BDO followed them with £81 billion ($110 billion) in total market valuation for its clients.

The rankings show audit firms have lost clients over the years as the overall number of businesses listed on the London Stock Exchange has fallen. The number of UK-listed companies has declined by almost 17% from 2020 until May of this year, Andrew Parson, Adviser Rankings’ managing director, said.

Meanwhile, client totals at PwC and BDO have both declined by about one-third from the second quarter of 2020 to the second quarter of 2025, the rankings found. KPMG has seen the biggest hit in clients among the auditors ranked, with an almost 50% fall in its number of UK-listed audit clients over the same time period.

These drops could be explained “by a move by some auditors to concentrate on the more profitable larger companies” as clients, as well as a general market contraction, Parson said by email. Tighter audit regulation has also made individual audits require more time and resources.

BDO is the largest auditor by market capitalization of smaller companies listed on the Alternative Investment Market, part of the London Stock Exchange tailored to smaller, higher risk firms. “In line with our strategy of controlled responsible growth, we remain focussed on the ongoing development of our listed client portfolio,” the firm said in an emailed statement.

PwC, also known as PricewaterhouseCoopers, and KPMG declined to comment.

The Big Four firms—Deloitte, Ernst & Young, KPMG, and PwC—continue to dominate audits of the largest UK businesses, including those that are part of the FTSE 100 index. The index tracks the largest 100 companies on the London Stock Exchange.

Only two FTSE 100 companies are audited by firms outside of the Big Four: BDO and Forvis Mazars.

However, the Big Four’s concentration on the biggest audit clients has opened the door to some mid-sized firms entering the market for smaller listed companies.

The government has promised to introduce audit reforms designed to break the Big Four’s dominance of large audits. There are now seven medium-sized audit firms with clients in the wider FTSE 350 index, led by BDO with 27, Adviser Rankings found.