The battle for AIM: Is PKF about to unseat BDO?

For years, BDO has dominated the AIM audit market, consistently holding the top spot in total clients and commanding a significant share of FTSE AIM 100 and UK 50 companies. But the latest Q1 2025 AIM Advisers Rankings Guide suggests that change is on the horizon.

PKF Littlejohn added three new AIM-listed clients this quarter, bringing it within just two clients of BDO. Meanwhile, Crowe gained ground in Health Care and Technology, while KPMG has overtaken Deloitte in market capitalisation rankings.

With competition intensifying, could 2025 be the year that the AIM audit pecking order experiences a major shift?

The Challengers: Who’s Closing in on BDO?

PKF is now at 89 AIM-listed clients, just two away from overtaking BDO’s 91 clients. The firm has a stronghold in the Basic Materials sector, with 39 clients—more than double BDO’s count. It also leads in Energy auditing, with 17 clients in that sector.

Additionally, PKF’s total AIM client market cap increased from £3.89B to £4.70B, indicating that its client base is expanding not just in number but also in value.

Crowe added two Health Care clients—ImmuPharma and Shield Therapeutics—which brought it into joint first place in the sector, alongside RSM UK Audit.

The firm has also strengthened its position in Technology auditing, where it is now tied with BDO, with both firms auditing 14 AIM-listed Technology companies.

While KPMG does not lead in client numbers, it has surpassed Deloitte in total AIM market capitalization, now ranking third at £7.56B. This shift suggests a focus on high-value AIM clients rather than volume.

The Incumbents: Can BDO Hold Its Ground?

BDO remains the top AIM auditor, with 91 clients, but its total market cap has slipped from £14.29B to £12.36B.

PwC is gaining ground in the FTSE AIM UK 50 rankings, now holding outright second place. Deloitte and Grant Thornton, meanwhile, are tied for third in the FTSE AIM 100 rankings.

As competition intensifies, client retention may become as important as client acquisition in determining who leads the AIM audit market in the months ahead.

The Shrinking AIM Market: What It Means for Auditors

One of the biggest challenges facing auditors is the ongoing decline in the number of AIM-listed companies. With fewer firms choosing to list on AIM, competition for auditing contracts is increasing.

This trend is also affecting brokers, law firms, and financial PR consultancies, forcing them to adapt their strategies in an increasingly competitive landscape. Despite this, some firms continue to expand. Strand Hanson, Allenby Capital, and Canaccord Genuity each added new clients this quarter, indicating that there is still growth potential for the right players.

The Verdict: Will We See a New AIM Audit Leader in 2025?

BDO remains the leading AIM auditor—for now. However, PKF Littlejohn is closing in fast, Crowe is making targeted gains in key industries, and KPMG is shifting its focus to higher-value clients.

With AIM itself evolving, the next few quarters will be crucial in determining whether BDO can maintain its leadership position—or if a new frontrunner will emerge.

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