The latest Adviser Rankings Ltd figures for AIM auditors reveal a quarter of mixed fortunes for firms across the rankings.
While PKF Littlejohn continues to lead by client numbers, PwC has overtaken BDO to claim the top position by aggregate market capitalisation of its clients, reflecting the strategic importance of a high-value client base over sheer volume.
PwC Gains Market Cap Lead from BDO
PwC’s rise to the top by market cap follows its appointment to Greatland Resources, a FTSE AIM 100 constituent.
This high-profile audit win significantly boosted PwC’s total client value, even as BDO maintained its lead in several other segments.
BDO had previously held the lead position by market cap, supported by a wide portfolio of AIM clients, including strength across Technology, Financials, and Consumer sectors. However, its growth this quarter was outpaced by PwC’s gains.
In the FTSE AIM UK 50, PwC also overtook Deloitte to take second place in client count, with BDO holding the top spot by market capitalisation.
Moore Kingston Smith’s Merger with Shipleys Alters the Mid-Tier Landscape
The standout development in this quarter’s rankings is the jump by Moore Kingston Smith, which doubled its AIM client numbers following the merger with Shipleys.
Announced in October 2024, the integration is now well advanced, and the firm has climbed ten places to equal 12th, sharing the spot with Forvis Mazars, Gravita Audit, and KPMG.
The merger has strengthened Moore Kingston Smith’s position in multiple sectors, reflecting a wider trend of consolidation among mid-tier audit firms.
Other firms benefiting from client gains include Kreston Reeves, which also enjoyed a positive quarter, as well as Cooper Parry Group and S&W, which made incremental moves up the rankings.
Meanwhile, Baker Tilly CI Audit, Gerald Edelman, and James Cowper Kreston entered the rankings for the first time.
Sector Leaders and Client Numbers
PKF Littlejohn remains dominant by client count across AIM, despite a net decline during the review period. It continues to hold an unrivalled lead in Basic Materials with 38 clients—more than double the number of BDO, its nearest competitor in the sector.
PKF also leads in Energy with 15 clients, underscoring its strong sector positioning.
BDO retains a strong foothold in Consumer Discretionary and Consumer Staples with 15 clients, and leads Technology with 11 clients, having overtaken Crowe in that category.
Crowe, despite an overall net decline, retains a competitive presence in several sectors and improved its ranking to standalone eighth in the FTSE AIM 100.
RSM UK Audit continues to lead Industrials (18 clients) and Health Care (10 clients) by client numbers, while also climbing to fourth place in the FTSE AIM 100, overtaking Deloitte.
FTSE AIM 100: PwC and BDO Battle for Value
Despite BDO’s client count gains in the FTSE AIM 100, it lost ground to PwC in terms of total client market value.
PwC’s newly acquired audit engagements, including Greatland Resources, allowed it to strengthen its high-value portfolio, positioning it ahead of BDO by aggregate market cap.
RSM UK Audit’s rise to fourth place and Crowe’s solid performance at eighth illustrate how firms outside the Big Four continue to challenge established hierarchies.
Regulatory Pressures Add to Market Dynamics
Beyond the rankings, regulatory considerations continue to shape the audit landscape.
The Association of Chartered Certified Accountants (ACCA) has urged the Financial Reporting Council (FRC) to adopt a more balanced approach to regulations affecting small and medium-sized enterprises (SMEs).
The FRC’s market study on SME audit accessibility highlighted concerns over backlogs, particularly for smaller companies, though AIM constituents have been less affected.
The regulatory environment remains a critical factor influencing auditor strategies and client relationships.
Sector-by-Sector Standouts
- Basic Materials: PKF Littlejohn’s 38 clients dominate the field.
- Energy: PKF also leads with 15 clients.
- Consumer Discretionary/Staples: BDO holds the lead with 15 clients.
- Financials & Real Estate: BDO remains strong with nine clients.
- Health Care: RSM UK Audit leads with 10 clients.
- Industrials: RSM UK Audit tops the table with 18 clients.
- Technology: BDO has taken first place from Crowe with 11 clients.
A Shifting Audit Market
The July 2025 AIM rankings underscore how the UK audit market continues to evolve.
Big Four firms remain dominant by market value, but mid-tier auditors are making notable gains through mergers, niche expertise, and targeted sector growth.