# Cybersecurity companies headquartered in London
Tamtam tracks 209 cybersecurity companies headquartered in London. This list ranks the 30 largest by number of employees on LinkedIn, led by BT Group, BAE Systems and Vodafone Business. Their median headcount is 688. Half of them were founded in 2005 or later.
These London-based companies specialize in cybersecurity, telecommunications, and IT services, representing a mix of large established corporations and mid-sized firms. Notable examples include BT Group, a global communications services company; BAE Systems, providing advanced technology-led defense and security solutions; Vodafone Business, offering mobile, fixed, and security services; and Noventiq, a digital transformation and cybersecurity provider.
The data shows a strong concentration of companies founded in the early 2000s, with Claranet (1996), BAE Systems (1999), Gamma (2002), and Mimecast (2003) illustrating this trend. This suggests a period of significant growth and development in these sectors within London.
π¬π§ London Β· 30 companies Β· Updated Nov 12, 2026
| # | Company | Industry | Headquarters | Employees | Founded |
|---|---|---|---|---|---|
| 1 | [BT Group](https://www.tamtam.ai/c/bt-group) (bt.com)
A global communications services company connecting people through technology to address challenges like the pandemic, climate change, and cyber security | Telecommunications | π¬π§ London | 73,712 | |
| 2 | [BAE Systems](https://www.tamtam.ai/c/bae-systems) (baesystems.com)
The company provides advanced technology-led defense, aerospace, and security solutions, with a skilled workforce in over 40 countries, focusing on innovation and long-term commitment | Defense and Space Manufacturing | π¬π§ London | 55,143 | 1999 |
| 3 | [Vodafone Business](https://www.tamtam.ai/c/vodafone-business) (vodafone.com)
Providing mobile, fixed, unified communications, IoT, cloud, and security services to businesses globally, regionally, and locally. | Telecommunications | π¬π§ London | 8,100 | |
| 4 | [Noventiq](https://www.tamtam.ai/c/noventiq) (noventiq.com)
A global digital transformation and cybersecurity solutions provider connecting 80,000+ organizations, with a diverse portfolio and active M&A strategy for growth | IT Services and IT Consulting | π¬π§ London | 3,941 | |
| 5 | [TryHackMe](https://www.tamtam.ai/c/tryhackme) (tryhackme.com)
It simplifies learning and teaching Cybersecurity through prebuilt courses and cloud-hosted virtual machines, ideal for CTFs, workshops, and training. | Computer and Network Security | π¬π§ London | 3,445 | 2018 |
| 6 | [Claranet](https://www.tamtam.ai/c/claranet) (claranet.com)
A global technology services provider offering managed services, professional services, and training in Cloud, Networks, Cyber Security, and Workplace technologies since 1996 | IT Services and IT Consulting | π¬π§ London | 3,073 | 1996 |
| 7 | [Quantum Security Agency](https://www.tamtam.ai/c/quantum-security-agency) (org.uk)
Specialized restaurant marketing agency offering solutions to help restaurants thrive through social media management, content marketing, websites, and other marketing services | Software Development | π¬π§ London | 2,842 | 2007 |
| 8 | [Gamma](https://www.tamtam.ai/c/gamma) (gammagroup.co)
Gamma is a leading supplier of Unified Communications services in the UK, Germany, Spain, and Benelux, offering robust solutions for communication and collaboration | Telecommunications | π¬π§ London | 2,588 | 2002 |
| 9 | [Mimecast](https://www.tamtam.ai/c/mimecast) (mimecast.com)
Protects humans, data, and AI agents through a unified platform, securing the workforce and their interactions with AI from cyberattacks. | Computer and Network Security | π¬π§ London | 2,396 | 2003 |
| 10 | [Cybersecurity](https://www.tamtam.ai/c/cybersecurity) (org.uk)
Cybersecurity experts providing incident response training, social engineering defense, vulnerability scanning, threat hunting, API testing, mobile app security, privacy compliance, user awareness training, and more | Computer and Network Security | π¬π§ London | 1,209 | 2017 |
| 11 | [Maintel](https://www.tamtam.ai/c/maintel) (maintel.co.uk)
Provider of cloud communications and managed services, specializing in digital transformation for public and private sectors Delivering digital workplace, customer experience, and secure connectivity solutions globally | Telecommunications | π¬π§ London | 946 | 1991 |
| 12 | [GCX](https://www.tamtam.ai/c/gcx) (gcxworld.com)
Network services enabling digital transformation through managed SD-WAN, hybrid networks, and extensive subsea cloud connectivity across emerging markets and Asia. | Telecommunications | π¬π§ London | 810 | 1988 |
| 13 | [Kerv](https://www.tamtam.ai/c/kerv) (kerv.com)
Kerv is a purpose-driven cloud and digital services organization providing enterprise software, consulting, networking, security, and digital transformation services across key industries | IT Services and IT Consulting | π¬π§ London | 782 | 2020 |
| 14 | [Beyond](https://www.tamtam.ai/c/beyond) (bynd.com)
A design agency focused on enhancing customer experiences through strategy, technology, and design, serving diverse clients globally with a remote-first workforce | IT Services and IT Consulting | π¬π§ London | 752 | 2010 |
| 15 | [Zenzero](https://www.tamtam.ai/c/zenzero) (zenzero.co.uk)
Design tailored IT infrastructure solutions using proven technologies to optimize client operations and maximize value from resources. | IT Services and IT Consulting | π¬π§ London | 688 | 2004 |
| 16 | [Options Technology](https://www.tamtam.ai/c/options-technology) (options-it.com)
Provides global financial technology solutions specializing in banking and trading infrastructure, integrating high-performance networking, cloud, security, and AI technologies. | IT Services and IT Consulting | π¬π§ London | 641 | 1993 |
| 17 | [TelefΓ³nica Tech (EN)](https://www.tamtam.ai/c/telefonica-tech-en) (telefonicatech.uk)
Specialist provider of integrated technology solutions including cybersecurity, cloud, data, AI, business applications, and digital workplace services. | IT Services and IT Consulting | π¬π§ London | 557 | |
| 18 | [Fortray Global Service Limited](https://www.tamtam.ai/c/fortray-global-service-limited) (fortray.com)
Provides services for digital transformation, cybersecurity, cloud, and managed IT. Also develops talent through tech and AI bootcamps for various digital skills. | IT Services and IT Consulting | π¬π§ London | 547 | 2011 |
| 19 | [Methods](https://www.tamtam.ai/c/methods) (methods.co.uk)
Digital transformation partner for UK public sector, specializing in helping government agencies improve services through innovative technology solutions and cost-saving strategies | IT Services and IT Consulting | π¬π§ London | 534 | 1990 |
| 20 | [SecurityHQ](https://www.tamtam.ai/c/securityhq) (securityhq.com)
It is a global cybersecurity company providing tailored solutions to enhance security posture and maximize cybersecurity investment for organizations. | IT Services and IT Consulting | π¬π§ London | 503 | 2003 |
| 21 | [Resillion](https://www.tamtam.ai/c/resillion) (resillion.com)
A global leader in quality engineering, testing, and cyber security services, providing end-to-end digital testing solutions with a dedication to success and cutting-edge technology | IT Services and IT Consulting | π¬π§ London | 479 | |
| 22 | [Yoti](https://www.tamtam.ai/c/yoti) (yoti.com)
privacy-focused identity verification and age verification solutions helping businesses and individuals build trust while reducing fraud and enhancing data control | Software Development | π¬π§ London | 454 | 2014 |
| 23 | [GL Noble Denton](https://www.tamtam.ai/c/gl-noble-denton) (dnvgl.com)
Global provider of risk management services dedicated to safeguarding life, property, and the environment, with a focus on safety, innovation, and sustainability | Oil and Gas | π¬π§ London | 423 | |
| 24 | [CREST](https://www.tamtam.ai/c/crest) (crest-approved.org)
An international organization ensuring quality in the global cyber security industry through accreditation, certification, and collaboration with various stakeholders worldwide | Computer and Network Security | π¬π§ London | 419 | |
| 25 | [MBA](https://www.tamtam.ai/c/mba) (mba-it.com)
IT solutions and services provider in London, specializing in complex applications, enterprise capabilities, and exceptional service for businesses in finance, legal, and insurance sectors | IT Services and IT Consulting | π¬π§ London | 388 | 2005 |
| 26 | [Police Digital Service](https://www.tamtam.ai/c/police-digital-service) (pds.police.uk)
The company coordinates and delivers digital services for UK policing to use technology for public safety, working with various organizations | IT Services and IT Consulting | π¬π§ London | 379 | 2015 |
| 27 | [S-RM](https://www.tamtam.ai/c/s-rm) (s-rminform.com)
It is a global intelligence and cyber security consultancy, providing critical decision-making support, resilience building, and crisis response for clients. | Security and Investigations | π¬π§ London | 373 | 2005 |
| 28 | [Pen AI](https://www.tamtam.ai/c/pen-ai) (gudens.com)
AI-powered writing tool with features like idea generation, content expansion, research assistance, overcoming writer's block, style control, grammar checking, and plagiarism detection Join the writing community | Computer and Network Security | π¬π§ London | 363 | |
| 29 | [Security Blue Team](https://www.tamtam.ai/c/security-blue-team) (centri.org)
It provides practical defensive cybersecurity training, free courses, certifications, and platforms like Blue Team Labs Online and CySec Careers. | Computer and Network Security | π¬π§ London | 354 | 2019 |
| 30 | [Kocho](https://www.tamtam.ai/c/kocho) (kocho.co.uk)
Empowering ambitious companies with Microsoft cloud solutions, identity, mobility, connectivity, and cyber security services for secure growth and business success | IT Services and IT Consulting | π¬π§ London | 332 | 2001 |
## How this list is built
Every company on this list has a Tamtam company profile. The industry is the one the company gives on LinkedIn; categories such as SaaS or fintech are classified by Tamtam's AI from the company's website and LinkedIn page; and the headquarters city must match the company's own address. Companies are ranked by the number of employees on LinkedIn, and the list is refreshed every night. Classifications can be wrong, so treat the list as a starting point rather than an official ranking. Last updated Nov 12, 2026.
## More company lists in London
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- [Marketing and communications agencies in London](https://www.tamtam.ai/l/marketing-agencies-london) (533)
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- [Hotel and hospitality groups in London](https://www.tamtam.ai/l/hospitality-groups-london) (445)
- [Luxury brands in London](https://www.tamtam.ai/l/luxury-brands-london) (428)
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## The same list elsewhere in United Kingdom
- [Cybersecurity companies in the United Kingdom](https://www.tamtam.ai/l/cybersecurity-companies-united-kingdom) (549)
## The same list elsewhere
- [Cybersecurity companies in the world](https://www.tamtam.ai/l/cybersecurity-companies-in-the-world) (3,776)
- [Cybersecurity companies in Europe](https://www.tamtam.ai/l/cybersecurity-companies-in-europe) (2,197)
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Source: https://www.tamtam.ai/l/cybersecurity-companies-london