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Top Cybersecurity companies in London

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

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

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

  1. 1
    Cloud Security Labs· London, England, United Kingdom
    • 3.5k employees
  2. 2
    TryHackMe· London, England, United Kingdom
    • 3.4k employees
    • Founded 2018
  3. 3
    Mimecast· London, England, United Kingdom
    • Post-IPO equity
    • 2.4k employees
    • Founded 2003
  4. 4
    Cybersecurity· Greater London, England, United Kingdom
    • 1.2k employees
    • Founded 2017
  5. 5
    Telos Corporation· Ashburn, Virginia, United States
    • Series unknown
    • 665 employees
    • Founded 1971
Reveal 221 more·100 free credits, no card

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 226 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: Sun, 21 Jun 2026 10:50:48 GMT

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