Moves to increase competition have failed to dent the Big Four’s auditing dominance, though smaller firms are showing signs of picking up higher-risk clients ditched by the biggest accounting firms.

“The Big Four have cornered the FTSE 100 market,” Steve Smith, research manager at Adviser Rankings Ltd, said in a phone call. He said that since May, the Big Four have audited every FTSE 100 company, the largest 100 companies on the Financial Times Stock Exchange. That’s the first time that’s happened in more than a decade.

Adviser Rankings figures released Sept. 2 showed a more even split of FTSE 100 audits among the Big Four than a decade ago. Mandatory auditor rotation is forcing big companies to change auditors more often. That is an opportunity for some smaller auditors to gain clients.

“EY has picked up FTSE 100 audit business in recent years,” Smith said, explaining that the market was now fairly evenly split between the Big Four as Ernst and Young LLP took business from the other big firms.

Of the Big Four, EY had the fewest FTSE 100 clients in August—22 compared to 18 in May. PwC, also known as PricewaterhouseCoopers LLP, was the biggest FTSE 100 auditor with 27 clients, down from 29 in May.

Deloitte LLP audited 26 FTSE 100 companies in August, and KPMG LLP 25, according to Adviser Rankings.

“The FTSE 100 rankings have never been closer,” Smith said. He pointed out that when Adviser Rankings started tracking the market in 2005, EY had just 19 clients and PwC 41, a gap of 22.

“The gap has narrowed to five, showing intense competition between the Big Four but there’s now no space for smaller firms,” Smith said.

The Leftovers

Despite gains by smaller accounting firms in the FTSE 250 market, the Big Four firms continue to dominate.

And given government attempts to bring smaller firms into the FTSE audit market, mid-sized firms increased their client numbers only modestly.

The Big Four controlled 95% of the FTSE 250 market by client numbers and 96% by market capitalization in August, according to Adviser Rankings.

PwC was the largest auditor of FTSE 250 companies, with 72 clients in August, two more than in May. EY was again the smallest of the Big Four but gained two clients in May-August to bring its total to 50.

BDO LLP had six FTSE 250 clients in August, the same number as Grant Thornton LLP and one more than in May.