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London is the UK’s largest market for audit and assurance services. The Big 4 firms alone generate over £18 billion in combined UK revenue, and more than 40 mid-tier and specialist audit firms operate across the city.
This guide compares 10 audit firms with a London presence, covering sector strengths, services offered, fee approach and the type of business each firm is best suited for. Each entry includes UK revenue, employee numbers and the specific differentiators that separate one firm from the next.
| Firm | Sector Strengths | Services Offered | Fee Approach | Best For |
| MMBA | FCA-regulated firms (CASS 5/CASS 7), SRA-regulated solicitors, ATOL travel, SMEs. | Audit and assurance, personal and corporate tax, SRA accountant’s reports, company secretarial, crypto tax. | Fixed-fee pricing; direct senior partner oversight on every engagement. | SMEs, regulated-sector businesses (legal, financial services, travel), owner-managed companies. |
| PwC | Financial services, capital markets, technology, energy, retail, healthcare. | Audit, assurance, tax, advisory, deals, consulting, ESG services. | Premium Big 4 pricing; enterprise-weighted fee structures. | FTSE 100 companies, multinationals, complex global structures requiring integrated advisory. |
| Deloitte | Technology, financial services, life sciences, manufacturing, public sector. | Audit, consulting, tax, risk advisory, digital transformation, cyber security. | Premium pricing; consulting-led model where audit feeds into higher-margin advisory. | Large corporates, digital transformations, Fortune 500 companies needing audit and consulting from one provider. |
| EY | Energy, healthcare, technology, financial services, consumer products. | Audit, tax, transaction advisory, consulting, strategy, sustainability reporting. | Premium Big 4 pricing; balanced audit and advisory fee split. | Large enterprises, sustainability-focused industries, cross-border transactions. |
| KPMG | Government, public sector, financial services, technology, healthcare. | Audit, tax, advisory, consulting, risk management, ESG consulting. | Premium pricing with strong European focus. | Public sector bodies, governance-heavy audit requirements, ESG-integrated reporting. |
| BDO | Real estate, energy, technology, hospitality, financial services, AIM-listed. | Audit, tax, advisory, business outsourcing, wealth management. | Mid-market competitive pricing; positioned between Big 4 and specialist firms. | AIM-listed companies, mid-market businesses (£10m–£500m turnover), owner-managed enterprises. |
| Grant Thornton | Mid-market generalist, PE-backed companies, retail, technology, not-for-profit. | Audit, tax, advisory, corporate finance, restructuring. | Mid-tier pricing; client-centric fixed-fee options available. | High-growth businesses, PE-backed companies, organisations approaching or completing IPO. |
| RSM | Consumer markets, family businesses, hospitality, retail, technology. | Audit, tax, risk advisory, financial management, succession planning. | Mid-market pricing; widest regional footprint of any mid-tier firm. | Family-owned businesses, mid-market companies, consumer and hospitality sectors. |
| Forvis Mazars | Financial services PIEs, retail, food, energy, healthcare, government, charities. | Audit, assurance, tax, advisory, consulting, sustainability, financial planning. | Mid-tier pricing; independent partnership model with global network access. | Financial services PIEs, international groups needing cross-border coordination, charities. |
| Evelyn Partners | HNW individuals, entrepreneurs, charities, private clients, professional practices. | Audit, tax, wealth management, financial planning, investment management. | Wealth-led pricing; combined professional services and investment management fees. | HNW business owners wanting audit, tax and wealth management from a single firm. |
This list includes the 4 largest audit firms globally (the Big 4), 4 established mid-tier firms with a significant London audit presence, a wealth-led firm with a strong professional services arm, and one specialist firm for SMEs and regulated businesses.
The ranking follows UK revenue rather than global revenue, because a firm’s UK operation determines the resources, partner availability and sector depth that London-based clients actually experience. The Big 4 dominate by revenue, but mid-tier and specialist firms often deliver a different kind of value: more partner contact time, fixed-fee structures and sector-specific expertise that larger firms reserve for their biggest clients.
MMBA is a chartered certified accountancy and registered audit firm with offices in London (Bloomsbury), Preston, Cambridge and Luton. The firm is ACCA-registered for audit and specialises in serving SMEs and businesses in regulated sectors.
MMBA’s audit services in London cover statutory audit, compliance audit, SRA client money audits, and FCA-regulated client engagements (including CASS 5 and CASS 7). The firm’s team includes professionals with prior experience at Big 4 and top-10 firms, bringing technical rigour to a smaller-firm environment where the senior partner oversees each engagement directly.
The firm’s differentiator is sector-specific regulatory audit. While the Big 4 and mid-tier firms handle FCA and SRA work as part of a broader portfolio, MMBA’s audit practice is built around these regulated engagements. Clients include solicitors’ practices requiring SRA accountant’s reports and FCA-authorised businesses needing CASS assurance.
MMBA is best suited to SMEs, owner-managed businesses, and regulated firms (legal and financial services) that want direct partner access, fixed-fee pricing and sector-specific audit expertise without the overhead of a larger firm.
PwC is the largest of the Big 4 firms, with a London headquarters at 1 Embankment Place and offices across the UK. The firm serves a client base that includes many of the world’s largest listed companies and multinationals.
PwC’s audit practice covers statutory audit, internal audit, regulatory compliance and financial statement assurance. The firm is strongest in financial services, capital markets, retail, technology and energy. PwC’s audit methodology integrates automated data testing and continuous monitoring tools, making it well suited to complex, multi-entity engagements.
The firm is best suited to FTSE-listed companies, large multinationals and organisations with complex multi-jurisdictional structures. Smaller businesses may find partner access limited and fee structures weighted towards large engagements.
Deloitte is one of the Big 4 firms, operating from its London base at New Street Square in Holborn with offices across the UK and globally. Deloitte is the largest professional services firm worldwide by revenue.
The firm’s audit approach is consulting-led, meaning audit engagements often serve as an entry point to wider advisory, risk and technology consulting work. Deloitte has invested heavily in AI-driven audit tools and data analytics platforms. Key sectors include technology, media and telecommunications, financial services, life sciences, and consumer products.
Deloitte is best suited to large corporates, organisations undergoing digital transformation, and businesses that want audit and advisory services from a single provider.
EY is a Big 4 firm operating from its London base at 1 More London Place, near London Bridge. The firm maintains a broad global presence and serves clients across regulated and sustainability-focused industries.
EY’s audit practice covers assurance, forensic and integrity services, and climate-related financial disclosure. The firm has been at the forefront of sustainability reporting, advising clients on ESG (Environmental, Social and Governance) disclosures and climate risk assessments. Key sectors include energy, healthcare, technology, government and financial services.
EY is best suited to companies in regulated or sustainability-focused industries where audit intersects with climate reporting and governance. The firm’s operating model provides a relatively high level of senior involvement in audits compared to other Big 4 firms.
KPMG is a Big 4 firm headquartered in the Netherlands but with a substantial UK practice operating from Canary Wharf in London. The firm has a particularly strong position in government, public sector and ESG advisory work.
KPMG’s audit practice covers statutory and regulatory audit, internal audit, IT audit and public sector assurance. The firm holds significant government framework contracts and leads on ESG consulting, helping organisations integrate environmental and social governance into financial reporting.
KPMG is best suited to public sector bodies, large corporates with governance-focused audit requirements, and organisations where ESG integration into the audit process is a priority.
BDO is the largest mid-tier audit firm in the UK, with its London office in Baker Street and a network of offices across the country. The firm occupies a distinct position between the Big 4 and smaller specialist practices.
BDO serves AIM-listed companies, mid-market businesses, owner-managed enterprises and international groups with UK operations. The firm’s audit teams work with clients whose needs sit in the mid-market segment, where the Big 4 are often either too expensive or too focused on larger clients to provide dedicated partner attention. Key sectors include real estate, energy, technology, hospitality and financial services.
BDO is best suited to mid-market businesses, AIM-listed companies and owner-managed enterprises that want Big 4 methodology without Big 4 pricing.
Grant Thornton is a mid-tier firm with its London practice operating from the Euston area and offices across the UK. The firm positions itself as the audit partner for high-growth, dynamic organisations.
Grant Thornton’s client base includes PE-backed businesses, scale-ups and companies approaching or recently completing an IPO. The firm merged with PKF in recent years, adding regional offices and expanding its sector coverage. Key sectors include technology, retail, real estate, and not-for-profit.
Grant Thornton is best suited to private equity-backed companies, fast-growing businesses, and organisations that want a named partner actively involved in the engagement rather than delegated to a manager.
RSM UK is a mid-tier firm with the widest regional footprint of any firm in its category, operating from offices across the UK. The firm targets the middle market with particular expertise in consumer businesses, family enterprises and hospitality.
RSM assists family-owned businesses with succession planning, governance, tax structuring and wealth management, making it a stronger fit than the Big 4 for businesses where personal ownership and family dynamics affect financial decision-making. Key sectors include consumer markets, retail, hospitality, technology, and family businesses.
RSM is best suited to mid-market and family-owned businesses that want a national firm with strong regional presence and sector-specific advisory alongside the audit.
Forvis Mazars is a mid-tier firm operating from its London base at 30 Old Bailey in the City, with offices across the UK. The firm joined the global Forvis Mazars network in 2024, giving UK clients access to cross-border audit and advisory capabilities across over 100 countries.
The firm’s audit practice is strongest in financial services, including public interest entities (PIEs), making Forvis Mazars one of the largest PIE auditors in the UK. The firm also serves clients in retail, food, energy, healthcare, government and the charity sector. Its most recent FRC inspection results confirmed strong audit quality outcomes.
Forvis Mazars is best suited to financial services PIEs, international groups needing cross-border audit coordination, charities, and mid-market businesses that want an independent firm with global reach and strong regulatory standing.
Evelyn Partners (formerly Tilney Smith & Williamson) is the UK’s largest integrated wealth management and professional services group. The firm operates from offices across the UK, Channel Islands and Ireland, with London headquarters at Gresham Street. NatWest Group completed its acquisition of Evelyn Partners in June 2026.
The firm’s professional services arm (inherited from Smith & Williamson) provides audit, accountancy, tax and advisory services. The audit practice is strongest for HNW individuals, entrepreneurs, owner-managed businesses, charities and not-for-profit organisations. The wealth management side offers financial planning, investment management and personal tax advice, making Evelyn Partners a natural fit for business owners who want personal and corporate finances managed by a single provider.
Evelyn Partners is best suited to HNW entrepreneurs and business owners who want audit, tax and wealth management from a single firm, particularly those with succession planning needs where personal and business finances intersect. Businesses considering Evelyn Partners should clarify how the NatWest ownership affects engagement terms and partner continuity going forward.
The decision depends on three factors: the complexity of your business, the regulatory environment you operate in, and how much direct partner involvement you need.
The Big 4 are the default choice. They have the global networks, the specialist teams and the FRC-inspected audit methodologies that institutional investors and regulators expect. PwC and Deloitte lead on consulting depth. EY leads on sustainability and ESG audit. KPMG leads on public sector and governance.
Mid-tier firms (BDO, Grant Thornton, RSM, Forvis Mazars) offer a strong alternative. Audit fees are typically lower, partner contact is more frequent, and sector specialisms are often deeper at this level. BDO is strongest for AIM-listed and international groups. Grant Thornton is strongest for PE-backed and high-growth companies. RSM is strongest for family businesses and consumer sectors. Forvis Mazars is strongest for financial services PIEs and businesses needing cross-border audit coordination. Evelyn Partners suits business owners who want audit and personal wealth management from a single firm.
Specialist firms provide the most practical and cost-effective audit. Firms like MMBA deliver statutory and regulatory audits with direct senior partner oversight, fixed-fee structures and sector-specific knowledge (SRA, FCA, ATOL) that larger firms typically reserve for their biggest clients.
Ask the firm who will sign off your audit. If the answer is a partner you have never met, the firm may be too large for your needs. If the answer is the same person who conducted your initial meeting, you are likely in the right place.
The best audit firms in London include Deloitte, PwC, EY, KPMG, Grant Thornton, BDO, RSM, and MMBA Accountants. These accountancy firms provide audit, tax, and advisory services across various industries, contributing significantly to the UK’s professional services sector.
Audit firms in the UK vary in size, with the Big Four leading in number of employees, number of partners, and revenue. Mid-tier firms like Grant Thornton and BDO also have a strong presence, while other firms like UHY Hacker Young, Begbies Traynor, and Haines Watts focus on niche markets.
Apart from audit and assurance, accounting firms in London provide tax planning, advisory services, mergers & acquisitions support, and wealth management. Firms like Kingston Smith and Evelyn Partners specialise in tailored financial solutions for businesses of all sizes.
The ranking of audit firms is based on their revenue, number of employees, and range of services. A table of the top firms typically includes the Big Four, followed by firms like BDO and RSM. Smaller firms, including Kingston Smith and Haines Watts, focus on specialised practices.
Mid-tier firms such as Grant Thornton and BDO continue to expand, while smaller firms like Begbies Traynor, UHY Hacker Young, and Haines Watts are gaining traction. These firms focus on mergers, tax advisory, and sector-specific practices, catering to a diverse client base.
The core audit standards (ISAs UK) are identical. Both Big 4 and mid-tier firms follow the same International Standards on Auditing issued by the Financial Reporting Council. The difference is in delivery. Big 4 firms use larger teams, more automation, and structured methodologies designed for complex, multi-entity groups. Mid-tier firms typically offer more direct partner involvement, faster turnaround and lower fees. The audit opinion carries the same legal weight regardless of which firm issues it.
Technically, yes. In practice, most Big 4 firms set minimum fee thresholds that make their services uneconomic for businesses with turnover below £10 million to £20 million. Small businesses that approach a Big 4 firm are often referred to an affiliated smaller practice or advised to seek a mid-tier or specialist firm. The audit quality for small businesses is typically higher with a firm whose operating model is designed for that client size.
The Financial Reporting Council inspects the audit quality of the largest UK firms annually and publishes the results. Look at the percentage of audits rated “good or limited improvements required” versus those requiring “significant improvements.” Also review whether the firm has received any formal sanctions or fines. FRC inspection results are published on the FRC’s website under Audit Quality Review reports and are free to access.
Several mid-tier firms are outpacing the Big 4 on percentage revenue increase. According to the Accountancy Today Top 30 ranking, Gravita recorded 75% year-on-year increase, Cooper Parry 60.4%, and MHA 56.5%. BDO’s revenue crossed the £1 billion mark. In comparison, the Big 4 reported single-digit percentage increases. The mid-tier segment is also being reshaped by private equity investment, with over 40 major UK firms now PE-backed or PE-owned.
