Top 10 Biggest Accounting Firms In UK 2026

The UK accounting sector remains one of the most competitive professional services markets in the world. With London serving as a global financial hub, the firms that operate here compete for blue-chip audits, complex tax mandates, and high-stakes advisory work. But the landscape is shifting. Technology adoption, ESG reporting requirements, and the ongoing fallout from audit reform debates have forced every firm to adapt.

To build this ranking, we weighed UK-specific revenue figures, professional headcount, market share data from industry analysts like IBISWorld, and each firm's strategic positioning heading into 2026. The Big Four still dominate the top slots, but the gap between them and the next tier is narrowing as mid-market specialists invest heavily in technology and sector expertise. Here are the 10 largest accounting firms in the UK for 2026.

These Are The Top 10 Biggest Accounting Firms In UK 2026:

1. Deloitte UK

Deloitte holds the top spot as the largest accounting and professional services network in the UK. The firm generates £5.6 billion in annual UK revenue and employs more than 26,000 professionals across 19 offices nationwide. That scale is difficult to overstate - Deloitte's UK practice alone would rank as a substantial enterprise in its own right.

The firm's focus on innovation sets it apart. Deloitte UK has poured significant investment into digital transformation, cybersecurity, and sustainability initiatives, positioning itself as a partner for clients navigating complex regulatory and technological change. Its client base spans the FTSE 100, public sector bodies, and fast-growing private companies.

Globally, Deloitte reported FY2025 revenue of $70.5 billion with approximately 473,000 employees worldwide, cementing its position as the world's largest accounting network. For UK businesses seeking a firm with unmatched resources and global reach, Deloitte remains the default choice.

2. PwC (PricewaterhouseCoopers) UK

PwC claims the distinction of holding the highest market share in the UK Accounting and Auditing industry, according to IBISWorld's 2026 industry analysis. That market leadership reflects the firm's deep penetration across the UK's largest corporations and public sector entities.

The firm's history is a story of mergers and longevity. PwC was formed in 1998 through the merger of Price Waterhouse and Coopers and Lybrand, though both predecessor firms trace their origins to the mid-1800s. That pedigree matters in a profession built on trust and continuity.

PwC operates in over 150 countries globally and reported global revenue of $56.9 billion for FY2025. Its UK practice, headquartered in London, remains one of the most prestigious employers for accounting and finance professionals in the country. For graduates and experienced hires alike, a PwC role carries significant weight on a CV.

3. EY (Ernst and Young) UK

EY ranks third among the UK's largest accounting firms, with a workforce exceeding 20,000 professionals. The firm delivers audit, assurance, tax compliance, financial transformation, and risk advisory services across a broad client base.

What distinguishes EY in the current market is its technology focus. The firm holds expertise in platforms including Microsoft Azure, SAP, Nvidia, Shopify, and UiPath, using automation, AI, and analytics to provide clients with real-time insights. That tech-forward approach resonates with clients who expect more than traditional compliance work.

EY's corporate history includes the 1989 merger of Ernst and Whinney with Arthur Young and Co., with roots extending back to the English firm Harding and Pullein, established in 1849. The firm reported global revenue of $53.2 billion for FY2025. EY has also positioned itself prominently in sustainability and ESG advisory, helping clients integrate environmental and social strategies into their core operations.

4. KPMG UK

KPMG is the fourth-largest accounting and auditing practice in the UK, having recorded 9% revenue growth in 2023 while expanding its workforce to approximately 18,000 employees. That growth trajectory suggests the firm has found its footing after a period of internal restructuring and strategic refocusing.

The firm was formed in 1987 when Peat Marwick merged with the Klynveld Main Goerdeler group, rebranding to simply KPMG in 1995. KPMG UK provides audit, tax, and advisory services with deep expertise across financial services, government, and corporate sectors.

Beyond its client work, KPMG is known for its commitment to professional development and its prominent sponsorship of the KPMG Women's PGA Championship. Global revenue stands at $39.8 billion. The firm's UK practice continues to compete aggressively for top-tier audit mandates, particularly in the financial services sector where it holds significant market share.

5. BDO UK

BDO is the largest global accounting network outside the Big Four, and its UK practice has carved out a distinct identity serving mid-sized businesses and public interest entities. The firm offers comprehensive tax support, CFO services, and statutory financial reporting.

What makes BDO particularly attractive to its client base is the balance it strikes. Companies that have outgrown local firms but find the Big Four too impersonal often land at BDO. The firm delivers more personalised service while maintaining international reach through its global network, which reported revenue of $14 billion.

BDO continues to expand its technology-enabled service offerings and sector-specific expertise across the UK market. For growing businesses that anticipate an eventual IPO or international expansion, BDO provides a credible pathway without the premium pricing of the Big Four.

6. RSM UK

RSM UK is a leading accounting firm specialising in the middle-market segment, offering extensive audit, tax, and consulting services with strong expertise in supporting medium-sized enterprises. The firm is part of the RSM International network, which ranks as the sixth-largest accounting network globally by revenue, with the network reporting $10 billion in global revenue.

The firm's UK practice has built a reputation for comprehensive business advisory services tailored to growing companies. Transaction advisory, restructuring, and technology consulting sit alongside traditional audit and tax work, giving clients a full-service experience.

RSM UK is particularly well-regarded for its sector-focused approach. Rather than trying to be everything to everyone, the firm has developed deep industry knowledge in areas like manufacturing, technology, and professional services, and it maintains a strong commitment to supporting entrepreneurial businesses.

7. Grant Thornton UK

Grant Thornton UK employs more than 5,000 professionals and delivers comprehensive tax support, CFO services, statutory financial statements, and month-end reporting services. The firm is particularly popular with mid-sized businesses and public interest entities.

Grant Thornton was founded in 1980 as a professional services network and operates across 147 markets globally with more than 68,000 employees. The network reported global revenue of $8 billion. The firm has extended its services into ESG advisory, financial due diligence, and operational improvement, broadening its appeal beyond traditional compliance work.

Technology plays a growing role in Grant Thornton's UK operations. The firm has integrated advanced tools including Dayshape, Leap, MS Power BI, and the Workday suite, blending sector expertise with digital innovation. That combination of human insight and automation capability positions the firm well for clients seeking efficiency alongside expertise.

8. Forvis Mazars UK

Forvis Mazars is a newly formed global network that combines the strengths of Forvis and Mazars in audit, tax, and advisory services. The UK practice, operating under the Mazars brand, provides an all-encompassing portfolio of services including accounting, tax, audit, and advisory for clients across dozens of industries.

The firm holds particular expertise in life sciences and healthcare, sectors that demand specialised knowledge and regulatory understanding. Forvis Mazars is also recognised for its outsourcing capabilities, helping companies optimise operations and reduce finance and payroll-related costs.

Governance is a notable strength. Forvis Mazars has independent non-executives serving on its Public Interest Committee, reflecting a commitment to transparency that resonates in a profession still rebuilding public trust. The firm was ranked number 10 among the most prestigious accounting firms in Vault's 2026 ranking, and the network reported global revenue of $5.2 billion.

9. Baker Tilly International

Baker Tilly International is an accounting network incorporated in London, England, with more than 700 offices around the world. Founded in 1987, the network has expanded to include commercial law and real estate advisory services alongside its auditing and accounting practices.

The network has experienced rapid expansion with robust assurance and consulting services, making it one of the fastest-growing networks in the accounting profession. Global revenue stands at $5.6 billion, placing it ahead of several larger-brand competitors in pure revenue terms.

Baker Tilly's UK presence is significant, with member firms serving clients across audit, tax, and business advisory services. For companies that need international reach but prefer working with locally rooted firms, Baker Tilly's network model offers a compelling alternative to the consolidated global giants.

10. Azets

Azets rounds out the top 10 UK accounting firms, providing technology-enabled accounting and advisory services with broad capabilities across payroll, tax, and business support. The firm is particularly well-suited for SMEs and expanding businesses.

What distinguishes Azets from the traditional firms above it is its modern, digitally-driven approach. The firm has built its model around cloud-based accounting, automated workflows, and real-time financial visibility, appealing to business owners who want more than an annual compliance exercise.

Azets has grown significantly in recent years through strategic acquisitions and organic expansion, establishing a strong presence across the UK. Its focus on technology adoption and client-centric service delivery makes it a popular choice for growing companies seeking a more agile accounting partner than the traditional firms can offer.