Company lists · Data refreshed September 2026
Top 25 Critical infrastructure defense based in the United Kingdom
RevenueBase identified 1,678 critical infrastructure defense headquartered in the United Kingdom as of September 2026 and tracks 114,619 professional contacts across them, including 10,570 with verified work emails. London is the largest hub.
This list covers critical infrastructure defense headquartered in the United Kingdom, matched on what each company actually does as described in its own words. Ranked by team size, largest first. Every row shows the company's own description, its RevenueBase Smart Search rating, and when it was last checked. Data refreshed September 16, 2026.
Published by RevenueBase, a B2B data infrastructure company. This list was built with RevenueBase Smart Search, the natural-language company search RevenueBase customers use to build their own targeted lists and unlock verified emails and direct dials at the companies on them. How these lists are built and judged.
The 25 largest critical infrastructure defense based in the United Kingdom
Ranked by team size| # | Company | Contacts | |||
|---|---|---|---|---|---|
| 1 | 79,699 contacts → | ||||
Indirect evidence “G4S is a leading security and facility services company that provides proactive security services and cutting-edge smart technology to deliver tailored, integrated security…” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 2 | 4,925 contacts → | ||||
Partial evidence “Sophos is a cybersecurity leader defending organizations globally with an AI-driven platform and expert-led services.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 3 | 1,508 contacts → | ||||
Indirect evidence “We are an intelligence-led security business.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 4 | 919 contacts → | ||||
Indirect evidence “CIS Security is an independent security company equipped to help customers to solve the complex challenges in today’s digital, connected and regulated business world.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 5 | 764 contacts → | ||||
Indirect evidence “MTI provides award-winning, end-to-end technology solutions and services in cyber security and data centre for over 35 years.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 6 | 679 contacts → | ||||
Partial evidence “At Roke, we stand at the forefront of defence and security, delivering cutting-edge intelligence and engineering solutions that protect nations, troops, borders, and businesses.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 7 | 597 contacts → | ||||
Indirect evidence “Part of ICTS Europe Group, ICTS UK & Ireland is a professional services firm which has been specialised in security risk for the past 39+ years.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 8 | 502 contacts → | ||||
Indirect evidence “SecurityHQ, a global cybersecurity company pioneering Security Performance Engineering for stronger operational performance and resilience.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 9 | 422 contacts → | ||||
Indirect evidence “Unlike traditional security providers, we're redefining what protection means in today's world.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 10 | 419 contacts → | ||||
Indirect evidence “Ward is an award winning, privately owned business, providing bespoke risk and security solutions including protective security personnel, explosive search dogs, narcotic search…” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 11 | 358 contacts → | ||||
Indirect evidence “ASEL design, develop and deliver fully bespoke and integrated security solutions, seamlessly bringing together people, technology and processes to achieve results-driven outcomes.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 12 | 303 contacts → | ||||
Strong evidence “Bridewell is the trusted cyber security partner for organisations operating within Critical National Infrastructure (CNI), as well as companies who want the highest standard of…” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 13 | 297 contacts → | ||||
Indirect evidence “At Quorum Cyber, we're on a mission to help good people win.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 14 | 246 contacts → | ||||
Indirect evidence “First Response Group (FRG) is one of the leading security, risk and FM providers in the UK delivering manned security, technology solutions, building management and vacant…” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 15 | 243 contacts → | ||||
Indirect evidence “Roc Technologies delivers transformational IT solutions to public and private sector organisations across the UK.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 16 | 242 contacts → | ||||
Indirect evidence “Obrela Security Industries is a global provider of cyber security services.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 17 | 205 contacts → | ||||
Indirect evidence “Pilgrims are a global security, risk management and service support company that identifies and manages risks for clients across all sectors, including oil & gas, telecoms…” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 18 | 200 contacts → | ||||
Indirect evidence “OpenView Security Solutions is the UK’S largest privately owned independent security company and provides unique, innovative and technologically excellent solutions to meet…” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 19 | 180 contacts → | ||||
Indirect evidence “Established in 1978, Bridgegate Security is proud to be one of the UK’s largest independent security contractors.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 20 | 177 contacts → | ||||
Indirect evidence “Whether you’re a business or an individual, digital threats to your precious data and assets can come in any form - external or internal.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 21 | 170 contacts → | ||||
Indirect evidence “DeterTech is an industry leading provider of highly innovative and intelligence-led end-to-end security solutions.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 22 | 170 contacts → | ||||
Indirect evidence “Looking after the things people care about, wherever they are’.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 23 | 168 contacts → | ||||
Indirect evidence “Sapphire delivers comprehensive cyber solutions tailored to your needs, spanning across consultancy, managed services, IT/OT and beyond.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 24 | 166 contacts → | ||||
Indirect evidence “We are GUK.” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
| 25 | 166 contacts → | ||||
Indirect evidence “Providing Exceptional Security Services to Corporate and Retail Customers - Brooknight Security, with over 30 years of experience, is the go-to choice for businesses seeking…” Source: RevenueBase Database · checked Sep 16, 2026Thanks. The Data Team will review it. | |||||
RevenueBase Smart Search
RevenueBase Smart Search assesses information from a company’s LinkedIn profile, information supplied directly by the company, its website, and other publicly available sources. It uses that information to rate how closely the company relates to this list’s category: critical infrastructure defense. Every row carries its rating and the description the rating was read from, so each one can be checked rather than taken on trust.
- Strong evidence
- The company's own public description of its business names critical infrastructure defense.
- Partial evidence
- Its own public description names part of critical infrastructure defense, so it works in or next to the category without describing itself that way.
- Indirect evidence
- The description shown does not name critical infrastructure defense. The match rests on the rest of the company's public profile rather than the one sentence quoted here, so this is the rating to check first.
RevenueBase Smart Search is how these lists are built: RevenueBase's data engine and AI assemble the companies that match a category defined in a user's own words, so a list can be about what companies actually do rather than about whichever industry code they were filed under.
Showing 25 of 1,678 critical infrastructure defense based in the United Kingdom
See the full list, filter by size, metro and specialty, and get verified emails and direct dials for all 10,570 reachable decision-makers.
Free signup · no credit card
Critical infrastructure defense based in the United Kingdom at a glance
As of Sep 16, 2026Companies by employee count
Email recency for this list is measured worldwide rather than for United Kingdom, so it is reported there. Company counts and contact totals on this page are exact for United Kingdom, over 1,678 companies.
How this list was built
Company categories are rarely black and white. RevenueBase reads each company's own description of its business to decide whether it belongs among critical infrastructure defense, so some rows will be adjacent to the category rather than pure plays. The description and RevenueBase Smart Search rating on every row are there so you can check each match yourself.
- Source
- The RevenueBase company graph: 60 million companies and 398.9 million professional contacts resolved from primary sources, queried with RevenueBase Smart Search, the natural-language company search available to every RevenueBase user.
- What qualifies
- Companies headquartered in the United Kingdom whose own description of what they do matches “critical infrastructure defense”. Matching reads each company's description, not its industry code or its name.
- RevenueBase Smart Search
- RevenueBase Smart Search is how this list is assembled and how each row is rated. RevenueBase's data engine and AI assess a company's LinkedIn profile, information supplied directly by the company, its website and other publicly available information, then relate it to a category defined in a user's own words. Each row is rated strong evidence (its own description names critical infrastructure defense), partial evidence (it names part of the category) or indirect evidence (the description shown names none of it and the match rests on the rest of the company's profile). The description supporting each rating is quoted on the row.
- What we exclude
- Companies whose own description does not clearly place them among critical infrastructure defense, and records with no verified work email. Companies headquartered outside United Kingdom are excluded even when they keep an office there.
- Match quality
- In blind human judging of this matching method, 86% of matched companies were on target. Expect roughly 1 in 7 rows to be adjacent to the category rather than a pure play. Every row shows the company's own description and its RevenueBase Smart Search rating so you can judge each match yourself. Read the full methodology: how the lists are built, how the judging worked, and what the figure means.
- Ranking
- Team size, largest first: companies are ordered by the number of professionals RevenueBase tracks at each one. Employee ranges shown are reported bands, for context.
- Verification
- Every listed company carries at least one verified work email, 10,570 across the full list. Contacts re-verify on a rolling cadence, and each contact's own verification date is shown inside RevenueBase.
- Refresh
- This page's figures were pulled from the company graph on September 16, 2026. Lists refresh periodically as the graph is re-checked.
- Corrections
- Wrong category, wrong headquarters, or a company that has closed? Use “Report an issue” on any row. Reports go to the RevenueBase Data Team and feed back into the company graph.
Critical infrastructure defense by metro
Frequently asked
What is RevenueBase Smart Search?
RevenueBase Smart Search is how RevenueBase decides which companies belong on this list and how strongly each one fits. Its data engine and AI assess a company's LinkedIn profile, information supplied directly by the company, its website and other publicly available information, then relate it to the category the list is about. Each row is rated strong evidence when the company's own description names critical infrastructure defense, partial evidence when it names part of the category, and indirect evidence when the description shown names none of it and the match rests on the rest of the company's profile.
How many critical infrastructure defense are there based in the United Kingdom?
RevenueBase identified 1,678 critical infrastructure defense headquartered in the United Kingdom as of September 2026, matched on each company's own description of what it does rather than its industry code.
What is the largest company on this list?
G4s, headquartered in London, tops this list with the largest team on record.
Which city has the most critical infrastructure defense?
London leads with 555 headquartered companies, followed by Manchester (49) and Birmingham (36).
How do I get contact information for these companies?
A free RevenueBase account lets you run this exact search and work the top results, verified emails and direct dials included. Upgrading unlocks all 10,570 verified decision-maker contacts tracked across these 1,678 companies.
How current is this list?
The list refreshes periodically as the company graph is re-checked. This page's figures were pulled on September 16, 2026.
Ready to reach these companies? Verified emails and direct dials for all 1,678 critical infrastructure defense based in the United Kingdom. Start with a free account, no credit card.
Download this list →Related lists
Critical infrastructure defense by geography
- Critical infrastructure defense based in Adelaide, Australia
- Critical infrastructure defense based in Brisbane, Australia
- Critical infrastructure defense based in Canberra, Australia
- Critical infrastructure defense based in Melbourne, Australia
- Critical infrastructure defense based in Perth, Australia
- Critical infrastructure defense based in Sydney, Australia
- Critical infrastructure defense based in Belo Horizonte, Brazil
- Critical infrastructure defense based in Brasilia, Brazil
- Critical infrastructure defense based in Curitiba, Brazil
- Critical infrastructure defense based in Porto Alegre, Brazil
- Critical infrastructure defense based in Rio De Janeiro, Brazil
- Critical infrastructure defense based in Sao Paulo, Brazil
Browse the directory
Browse: Companies home · All United Kingdom lists · All Critical infrastructure defense lists · New lists
About this data
RevenueBase is a B2B data infrastructure company. Its company graph covers 60 million companies and 398.9 million professional contacts, with emails verified on a rolling cadence rather than scraped once and left to decay. These company lists are generated directly from that graph with RevenueBase Smart Search, the same natural-language company search every RevenueBase user has: describe a market in plain words, get the companies that match, and add verified emails and direct dials for the people at them. It is the same data that powers RevenueBase's B2B data products, and a free account includes 500 credits to start. How these lists are built and judged.
More company lists
- All company lists
- Lists by location
- Lists A-Z
- New lists
- Critical infrastructure defense based in Adelaide, Australia
- Critical infrastructure defense based in Brisbane, Australia
- Critical infrastructure defense based in Canberra, Australia
- Critical infrastructure defense based in Melbourne, Australia
- Critical infrastructure defense based in Perth, Australia
- Critical infrastructure defense based in Sydney, Australia