For many years mid-tier firms have harboured ambitions of edging closer to the top of the audit premier league. But while they have occasionally secured a marquee client or persuaded a partner or even an entire team to jump ship, the gulf in scale, investment and international reach between them and the Big Four has remained stubbornly wide. Until recently, few expected that dynamic to change in any material way.
The past year and a half has shifted that perception, with the most assertive attempts to date to narrow the distance between the middle and top end of the market.
Doubling up
Late in 2024, Grant Thornton’s US arm announced a formal merger with its Irish firm, backed by private equity group New Mountain Capital. It was presented not as a one-and-done merger but the first step in a wider restructuring designed to recalibrate the network’s global operations. In the months that followed, the firm added new member practices and began to articulate plans that were more coordinated, and more ambitious, than anything it had signalled previously.
The mid-tier majors are no longer content to be on the ranking fringes
A second, more surprising jolt came with BDO’s announcement in October that its Irish and UK partnerships plan to merge. The move cements the mid-tier firm’s fifth-place ranking, just outside the Big Four, and clarifies its intention to push on further. The combined entity has revenues exceeding £1.1bn, with around 8,500 staff and more than 500 partners across 20 offices. The integration sends a message that the mid-tier’s largest players are no longer content to operate on the fringes of the rankings.
What clients want
Nor is the trend limited to these two networks. Earlier this year, MHA became the first UK accountancy firm of its scale to list on the London Stock Exchange. Its chief executive Rakesh Shaunak described the listing as a platform for consolidation, and reiterated in the firm’s interim results in November that clients increasingly expect scale, depth and cross-border service.
It is a view widely shared among CFOs and boards. Clients want evidence a firm can deliver work to a uniform standard across jurisdictions.
That expectation places pressure on the traditional network approach, which typically involves loose structures that rely on shared branding, high-profile annual conferences and voluntary alignment. Those arrangements made sense in an earlier era, but the demands of multinational clients and the scrutiny of regulators have moved on.
Reg and tech
Public interest audits now command extensive requirements. Regulators have become less tolerant of loose affiliations that behave more like franchises than cohesive global organisations.
Consolidation is the only practical route to fund the tech requirement
Technology is accelerating the shift. Audit has become an even more data-driven exercise, dependent on platforms capable of testing high volumes of transactions and flagging anomalies in real time. The Big Four’s investment is measured in billions. Their mid-tier rivals, operating without unified structures, struggle to match that pace. Consolidation is emerging as the only practical route to funding the technology spending required for modern assurance. Without it, firms risk falling behind, not because of lack of expertise but because necessary expenditure has grown prohibitively costly.
Talent tempters
Talent is another factor. While the Big Four remain magnets for graduates, mid-tier firms are finding new ways to differentiate themselves. The prospect of partnership retains value, but private equity involvement has introduced additional incentives and more flexible career paths. For some recruits, the blend of progression, culture and potential to cash out their equity is proving persuasive.
Mandatory audit rotation will create opportunities
At the same time, the Big Four face challenges of their own. Regulatory scrutiny continues to intensify, rules on conflicts of interest are tightening, and several markets are debating structural reforms that could reshape how firms operate. Mandatory audit rotation will create opportunities over the coming years. Mid-tier firms that have consolidated their platforms and can demonstrate true international scale will be better positioned to compete for engagements that were once out of reach.
Expect 2026 to see a lot more deals. Change will not be immediate, but the direction of travel is clear. And as often happens, when the momentum of consolidation builds, it is unlikely to reverse.
