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Top Cybersecurity companies in London

Companies defending or attacking software, networks, and cloud infrastructure. Filtered to companies headquartered in London.

Built from a search like: “Top Cybersecurity companies in London”

Ranked by current headcount across Cybersecurity companies headquartered in London. Refreshed daily.

  1. 1
    TryHackMe· London, England, United Kingdom
    • 3.3k employees
    • Founded 2018
  2. 2
    Mimecast· London, England, United Kingdom
    • Post-IPO equity
    • 2.5k employees
    • Founded 2003
  3. 3
    Cybersecurity· Greater London, England, United Kingdom
    • 1.2k employees
    • Founded 2017
  4. 4
    Telos Corporation· Ashburn, Virginia, United States
    • Series unknown
    • 661 employees
    • Founded 1971
  5. 5
    CREST· London, England, United Kingdom
    • Grant
    • 392 employees
    • Founded 2006
  6. 6
    Security Blue Team· London, England, United Kingdom
    • 349 employees
    • Founded 2019
  7. 7
    COFENSE· Ashburn, Virginia, United States
    • Debt
    • 291 employees
    • Founded 2011
  8. 8
    Callsign· London Colney, England, United Kingdom
    • Series unknown
    • 273 employees
    • Founded 2011
  9. 9
    CyberSolve· Sterling, Virginia, United States
    • 257 employees
    • Founded 2016
  10. 10
    Secon· London, England, United Kingdom
    • Grant
    • 218 employees
    • Founded 1999
  11. 11
    Cybersecurity Community· London, England, United Kingdom
    • 199 employees
  12. 12
    Glasswall· London, England, United Kingdom
    • Private equity
    • 165 employees
    • Founded 2005
  13. 13
    Open-Source Security· London, England, United Kingdom
    • 160 employees
  14. 14
    Gudens Cybersecurity· London, England, United Kingdom
    • 132 employees
    • Founded 2022
  15. 15
    CDN77· London, England, United Kingdom
    • 126 employees
    • Founded 2011
  16. 16
    Infinigate UK & Ireland· London, England, United Kingdom
    • 124 employees
    • Founded 2001
  17. 17
    Bulletproof (Cyber Security)· London, England, United Kingdom
    • 118 employees
    • Founded 2016
  18. 18
    Electronic City· Linden, New Jersey, United States
    • 110 employees
  19. 19
    Information Security Forum· London, England, United Kingdom
    • 103 employees
    • Founded 1989
  20. 20
    CyberOne· London, England, United Kingdom
    • 94 employees
    • Founded 2005
  21. 21
    Infosec Ventures· London, England, United Kingdom
    • 92 employees
  22. 22
    White Hat (an EPAM company)· London, England, United Kingdom
    • 91 employees
    • Founded 2012
  23. 23
    e92plus· Surbiton, England, United Kingdom
    • 89 employees
    • Founded 1989
  24. 24
    Risk Ledger· London, England, United Kingdom
    • Series A
    • 85 employees
    • Founded 2018
  25. 25
    Intruder· London, England, United Kingdom
    • Seed
    • 85 employees
    • Founded 2015

Find engineers at Cybersecurity companies in London

London has long been a hub for Cybersecurity, and the list above ranks the largest Cybersecurity companies headquartered there by current headcount, drawn from public LinkedIn and Crunchbase records. With 224 matching companies in our index, this is a good map of where the Cybersecurity talent in Londonlives — useful whether you’re recruiting, partnering, or sizing a market.

The biggest Cybersecurity companies in London tend to be the gravitational centres for specialised talent — senior engineers, ML researchers, applied scientists, designers — while the smaller ones compete on speed, equity, and proximity to founders.

Refolk converts this list into a live search. Ask for “Cybersecurity engineers in Londonhiring senior staff” or “founders of Cybersecurity companies in Londonwho left in the last 12 months” and Refolk returns a ranked shortlist with the evidence that earned each person a spot.

How this list is built

Refolk pulled Cybersecurity companies headquartered in London from public LinkedIn and Crunchbase records, ranked them by current employee count, and kept those with at least 10 employees. The list refreshes once a day.

Last refreshed: Thu, 07 May 2026 08:38:10 GMT

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