Choosing an audit firm is one of the most consequential finance decisions a business makes. It affects your audit quality, your relationship with regulators and investors, the fee you pay, and the calibre of advice you get beyond the audit opinion. But the decision is rarely straightforward, because the audit market isn’t one market – it’s several, divided roughly into three tiers.
This guide compares Big 4 firms, mid-tier firms, and smaller independent practices from the perspective of the client – the finance director, the board, the audit committee chair – rather than the employee. If you’re deciding who should audit your company, this is what actually matters.
What are the Big 4 accounting firms?
The Big 4 are Deloitte, EY (Ernst & Young), KPMG and PwC (PricewaterhouseCoopers). Together they audit around 97% of FTSE 350 companies and dominate the public interest entity (PIE) audit market globally.
Each Big 4 firm employs between 300,000 and 400,000 people worldwide and generates annual revenues measured in tens of billions. In the UK, they are the default choice for large listed companies, major financial institutions, and businesses with complex international structures.
What the Big 4 offer:
- Global reach. If your group has subsidiaries in 15 countries, a Big 4 firm can audit all of them under one engagement letter. No mid-tier firm can match that scale.
- Brand credibility with institutional stakeholders. Some banks, PE houses and institutional investors specify a Big 4 audit as a condition of funding. It’s not about quality – it’s about signalling.
- Deep technical resources. Complex accounting issues (IFRS 15 revenue recognition, IFRS 16 lease accounting, financial instruments) can be referred to internal specialist teams.
- Regulatory expectations. For PIEs, financial services firms and other regulated entities, the FRC inspects Big 4 audits more frequently. That scrutiny drives higher technical standards, though it also drives higher fees.
The trade-offs of using a Big 4 audit firm
Big 4 firms are built for scale, and scale comes with trade-offs that directly affect you as a client:
Cost. Big 4 audit fees are often significantly higher than mid-tier equivalents for comparable work. The overhead of global offices, consultancy divisions, and brand marketing gets passed through to audit clients. For a private company turning over £10m-£30m, the fee difference between a Big 4 firm and a mid-tier alternative can be substantial.
Junior staffing. The Big 4 model relies on high volumes of graduate trainees doing the fieldwork. Your audit partner might be brilliant, but you’ll see them for half a day at planning and half a day at completion. The rest of the time, you’re dealing with staff in their first or second year of training who are still learning how to audit, let alone how to understand your business.
Partner inaccessibility. Each Big 4 partner manages a portfolio of 15-25 audit clients. They simply don’t have time to be involved in the detail of your audit. If you call your audit partner with a question, you’re more likely to get a callback from a manager or senior.
Staff turnover. The Big 4 operate a well-documented “up or out” model, where trainees either make partner or leave. Salary expectations rise sharply after qualification, so experienced staff often move on. The people who did your audit last year may have left the firm by the time this year’s fieldwork starts. You end up explaining your business from scratch every year.
Over-engineered for mid-market. Big 4 audit methodologies are designed for FTSE 100 complexity. When applied to a private company with £15m turnover, the process can feel disproportionate – more documentation, more forms, more review layers than the engagement actually requires.
What do mid-tier audit firms offer?
Mid-tier firms in the UK include Grant Thornton, BDO, RSM, Mazars, Crowe, Moore Kingston Smith, Saffery Champness, and a range of regional firms with strong audit practices. Some of these (Grant Thornton, BDO, RSM) have international networks; others specialise in UK domestic audit.
What mid-tier firms tend to do differently:
- Partner-led delivery. In a mid-tier firm, the audit partner is typically involved in planning, fieldwork review, and completion. You deal with a senior person who knows your business, not a chain of proxies.
- Team continuity. Smaller firms have lower staff turnover than the Big 4. The same audit manager and senior will often work on your audit for three, four, five years running. They learn your business and stop asking the same questions.
- Proportionate methodology. Mid-tier firms apply the same International Standards on Auditing (ISAs) as the Big 4, but their approach tends to be more proportionate to the size and complexity of the client. Less paperwork, more judgement.
- Sector specialism. Many mid-tier accounting firms specialise in niche sectors – charities, solicitors, technology, healthcare, property – and have deeper expertise than a Big 4 generalist team. Firms tend to build genuine depth in their chosen sectors rather than trying to cover everything.
- Fixed fees. Mid-tier firms are more likely to offer genuinely fixed audit fees rather than time-based estimates.
- Practical management letters. Because the partner actually knows your business, the management letter tends to contain specific, actionable recommendations rather than boilerplate observations.
What about smaller independent firms?
Below the mid-tier, there are thousands of smaller accounting firms across the UK that hold audit registration. Sole practitioners, two-partner firms, and local accountancy practices can all sign statutory audit opinions provided they are registered with a recognised supervisory body (ICAEW, ACCA, or ICAS).
Smaller firms can offer the lowest fees and the most personal service. The risk is capacity and resilience – if your audit partner is on holiday or ill, who steps in? For regulated or complex audits, a smaller firm may lack the specialist technical resources to handle unusual issues efficiently.
That said, for a straightforward single-entity audit of a private company with turnover under £5m, a well-run smaller firm can deliver an excellent audit at a very competitive fee.
The PE-backed accountancy firm question
Since 2020, private equity has invested heavily in UK accountancy. Firms like Azets (Cogital Group), Sumer Group (formerly Baldwins), and Evelyn Partners (formerly Tilney Smith & Williamson) have been through PE-backed consolidation. Cooper Parry took investment from Carlyle Group in 2024.
What does this mean for you as an audit client?
- Standardisation. PE-backed firms tend to standardise processes, technology and service delivery across the group. This can improve efficiency but can also reduce the flexibility that made the firm attractive in the first place.
- Staff turnover. Mergers and integrations often lead to staff departures. The people who built the relationship with you may leave during or after the integration.
- Cross-selling pressure. PE investors expect growth, and one way to achieve it is to sell additional services (tax, advisory, consultancy) to existing audit clients. This can create tensions with auditor independence rules.
- Fee increases. PE-backed firms need to hit margin targets. Audit fees may rise faster than at firms that aren’t under that pressure.
None of this means PE-backed firms deliver bad audits. But it’s worth asking: who owns your accounting firm, and how does that ownership structure affect the consultancy culture and the service you get as an audit client?
Is Grant Thornton a mid-tier firm?
Grant Thornton is technically the fifth-largest accounting firm in the UK by revenue, sitting just below the Big 4. They audit some FTSE 350 companies and have a substantial public sector and financial services practice. In market positioning, they sit between the Big 4 and the mid-tier – sometimes called “the fifth firm” or part of the “Big 5”.
BDO and RSM are the next largest, followed by Mazars, Crowe, and a group of strong regional and specialist firms.
For practical purposes, if you’re choosing between Grant Thornton and a Big 4 firm, the decision factors are similar to the Big 4 vs mid-tier comparison: cost, partner access, team continuity, and sector expertise.
How to decide which type of audit firm is right for you
The right audit firm depends on your specific situation, not on firm size alone. Consider these factors:
| Factor | Favours Big 4 | Favours mid-tier / independent |
|---|---|---|
| Listed or planning to list | Yes – institutional expectation | No |
| International group (10+ countries) | Yes – global network needed | Depends on network |
| Annual turnover under £50m | Rarely | Yes – proportionate service |
| Regulated sector (FCA, SRA, Charities) | Yes if PIE | Yes if specialist expertise |
| Want partner involvement | Limited | Yes – standard at mid-tier |
| Budget-sensitive | No | Yes – often significantly less |
| PE/VC-backed and growing | Yes if exit involves institutional buyers | Yes for current stage |
| Value team continuity | No – high turnover | Yes – lower turnover |
If you’re a private company with turnover between £5m and £50m, not listed, not planning an IPO, and not required by your stakeholders to use a Big 4 firm, a mid-tier or specialist audit firm will almost always give you better value and a better audit experience.
Where Audit Group fits
We’re the audit arm of Jack Ross Chartered Accountants, a Manchester-based ICAEW-regulated practice established in 1948. We audit companies, charities, solicitors’ practices, pension schemes and foreign subsidiaries across the UK.
Our audit partners lead every engagement personally. We quote fixed fees, we don’t rotate junior staff annually, and we write management letters that contain actual recommendations for your business rather than generic observations. We’re registered on the Register of Statutory Auditors.
If you’re currently with a Big 4 firm and questioning whether you’re getting value for money, or you’re with a smaller firm and need more technical depth, we’d welcome a conversation. No obligation – just an honest assessment of whether we’re the right fit.
Call 0161 832 4451 or request a proposal below.
