The Largest Accountancy Firms in the UK (2025 Edition)



When it comes to targeting accountants, understanding the landscape of the largest accountancy firms in the UK is crucial for any business looking to expand its B2B reach. Size matters in accountancy—not only because larger firms offer a wider scope of services and carry considerable reputational weight, but also due to their extensive employee base, which provides a rich network for marketing and sales efforts.

In 2025, the UK accountancy sector is undergoing rapid change. Mergers and acquisitions (M&A), digitalisation, and audit reforms are reshaping how firms operate and engage with clients. For businesses aiming to connect with professionals in this field, targeting the largest accountancy firms presents an excellent opportunity to access decision-makers and influencers at scale.

This blog draws on publicly available data from 2024–2025 to present a definitive list of the largest accountancy firms in the UK. Whether you are a B2B marketer, recruiter, or supplier, understanding this list and leveraging quality contacts from these firms can accelerate your outreach strategy and improve lead generation.

The Top 10 Largest Accountancy Firms in the UK (2025)

1. Deloitte

Revenue (2024–25): £4.5bn
Employees: 22,000+ UK-based
HQ: London

Deloitte leads the list of the largest accountancy firms with a diverse service portfolio spanning audit, tax, advisory, and technology. For B2B marketers, Deloitte’s large workforce and broad industry reach represent a prime target segment. Utilising a high-quality B2B contacts database focused on Deloitte can enable precise outreach to key decision-makers, enhancing campaign effectiveness.

2. PwC

Revenue (2024–25): £4.2bn
Employees: 21,500+ UK-based
HQ: London

PwC is a titan in consulting, audit, and deal advisory services. For companies aiming to engage accountants in these areas, targeting PwC’s extensive UK staff is essential. Access to verified contacts within PwC through specialist databases can provide unparalleled insights and open doors to strategic partnerships.

3. KPMG

Revenue (2024–25): £3.7bn
Employees: 19,000+ UK-based
HQ: London

Known for audit, tax, and advisory, KPMG remains one of the largest accountancy firms with a strong focus on compliance and ESG services. Businesses looking to market to KPMG accountants benefit hugely from detailed contact databases that allow segmenting by specialism and seniority.

4. EY (Ernst & Young)

Revenue (2024–25): £3.6bn
Employees: 18,500+ UK-based
HQ: London

EY’s innovative approach to blockchain auditing and AI-powered risk assessments makes it a magnet for technology vendors and advisory services. Targeted marketing campaigns, driven by accurate EY contacts data, can maximise engagement within this fast-evolving environment.

5. BDO

Revenue (2024–25): £1.1bn
Employees: 6,000+ UK-based
HQ: Birmingham

BDO, a leading mid-tier firm and one of the largest accountancy firms in the UK outside the Big Four, serves many SMEs. This makes BDO a key focus for businesses targeting smaller enterprises through their accountants. Our B2B contact databases help you connect directly with influential BDO partners and managers.

6. Grant Thornton

Revenue (2024–25): £900m
Employees: 4,500+ UK-based
HQ: London

Grant Thornton’s entrepreneurial culture and sector focus on technology and healthcare offer rich opportunities for specialised marketing. Reaching the right contacts here requires access to detailed and up-to-date data—a service our company specialises in delivering.

7. Mazars

Revenue (2024–25): £700m
Employees: 3,700+ UK-based
HQ: London

Mazars is expanding rapidly, making it another crucial target for B2B marketers. Leveraging our contacts database allows businesses to tap into Mazars’ international network and client base with precision.

8. RSM

Revenue (2024–25): £650m
Employees: 3,200+ UK-based
HQ: London

RSM’s focus on sustainability advisory and cloud accounting positions it well within modern client needs. Connecting with RSM’s key professionals through a reliable contacts database can streamline outreach and boost conversion rates.

9. Smith & Williamson

Revenue (2024–25): £550m
Employees: 2,800+ UK-based
HQ: London

The merger with Tilney has positioned Smith & Williamson as a unique player combining wealth management and accounting. For firms targeting these combined service areas, our curated contact lists ensure campaigns reach the right professionals.

10. Moore UK

Revenue (2024–25): £500m
Employees: 2,500+ UK-based
HQ: London

Moore UK offers personalised services typical of challenger firms among the largest accountancy firms. Targeting Moore UK’s decision-makers with relevant messaging is made more effective when supported by high-quality contact data.

Notable Mentions: Firms on the Rise

Aside from the established giants, fast-growing firms like Evelyn Partners, PKF, and UHY Hacker Young are increasing their market share. They are often the go-to firms for specific sectors or regional markets. Our comprehensive UK accountants database includes contacts from these rising challengers, enabling you to diversify your targeting strategies beyond the largest accountancy firms.

Why Size Isn’t Everything

While the largest accountancy firms dominate in size and revenue, many clients prefer smaller or specialist firms for their flexibility and niche expertise. Regardless, if your goal is to market to accountants, having access to detailed B2B contacts across the full spectrum—from the largest accountancy firms to emerging players—is vital.

To help you succeed, our Accountants Database contains over 500 firms segmented by size, location, and specialism. This resource is specifically designed for B2B marketers, recruiters, and suppliers who want to engage accountants effectively. Whether you want to focus on the Big Four or target niche firms, our database ensures you reach the right people with precision.

 Conclusion

The landscape of the largest accountancy firms in the UK continues to evolve rapidly, driven by innovation, regulatory changes, and shifting client demands. Whether you’re aiming to connect with the Big Four giants or ambitious national players, understanding who these key firms are—and having direct access to their decision-makers—can make all the difference in your B2B marketing strategy.

That’s where a comprehensive, accurate UK accountants' contacts database becomes indispensable. By leveraging up-to-date data on the largest accountancy firms and their key personnel, your business can engage more effectively, generate higher-quality leads, and ultimately accelerate growth.

If you’re serious about targeting accountants within the largest accountancy firms in the UK, our expertly curated database is designed to help you cut through the noise and reach the right contacts with confidence. Explore our UK Accountants Database today to transform your outreach and secure meaningful connections across the sector.


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