While 13% of FTSE 350 audits are carried out by mid-tier and challenger audit firms, these account for only 2% of total audit fees at £28m.

The total accumulative audit fees for the FTSE 350 was £1.4bn in 2023, but 98% of these fees were earned by the Big Four of PwC, Deloitte, EY and KPMG. They continue to dominate audit with an 87% market share.

Mid-tiers have only grown their share of audit business by 2% in the previous year from 11% in 2022. BDO and Forvis Mazars earned just over 4% of total listed audit fees each, while the remaining 2% was split between the remaining firms, showed analysis from the Financial Reporting Council (FRC).