Company lists · Data refreshed September 2026

Top 25 Critical infrastructure defense based in London, United Kingdom

Name: Critical infrastructure defense based in London, United Kingdom
Creator: RevenueBase
License: https://creativecommons.org/licenses/by/4.0/

Compiled by the RevenueBase Data Team Data refreshed Sep 16, 2026 555 companies tracked

RevenueBase identified 555 critical infrastructure defense headquartered in London, United Kingdom as of September 2026 and tracks 89,286 professional contacts across them, including 2,507 with verified work emails. London is the largest hub.

This list covers critical infrastructure defense headquartered in London, 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.

How to read this list HQ checked on every row RevenueBase Smart Search rating on every row Refreshed Sep 16, 2026 86% judged on-target in blind review

555Companies

89,286Contacts tracked

2,507Verified emails

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The 25 largest critical infrastructure defense based in London, United Kingdom

Ranked by team size

Top 25 of 555 critical infrastructure defense based in London, United Kingdom, ranked by team size, largest first. Data refreshed Sep 16, 2026. RevenueBase Smart Search rates how each company's information relates to critical infrastructure defense: strong evidence (its own description names it), partial (names part of it), indirect (matched on the rest of its profile rather than the description shown). Click a contact count to view that company's people.
#	Company	RevenueBase Smart Search	Headquarters	Employees	Contacts
1	G4s	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	10001+	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, 2026
2	CIS Security Limited	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	1,001-5,000	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, 2026
3	Ward Security	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	1,001-5,000	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, 2026
4	Argenbright Security Europe Limited - Asel	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	5,001-10,000	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, 2026
5	Obrela	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	201-500	242 contacts →
	Indirect evidence “Obrela Security Industries is a global provider of cyber security services.” Source: RevenueBase Database · checked Sep 16, 2026
6	Deepcytes Cyber Labs UK	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	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, 2026
7	QCIC	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	159 contacts →
	Indirect evidence “QCIC is an award-winning global engineering firm specialising in designing, building and running security systems.” Source: RevenueBase Database · checked Sep 16, 2026
8	The Keyholding Company	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	137 contacts →
	Indirect evidence “The Keyholding Company are a tech-enabled mobile security services company, specialising in alarm response, mobile patrols, locks and unlocks, emergency and temporary guarding…” Source: RevenueBase Database · checked Sep 16, 2026
9	Trpglobal	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	126 contacts →
	Indirect evidence “We are TRPGLOBAL, your strategic partner in helping you with the complexities of risk management.” Source: RevenueBase Database · checked Sep 16, 2026
10	Bulletproof Cyber Security	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	123 contacts →
	Indirect evidence “Bulletproof is now part of WorkNest Secure.” Source: RevenueBase Database · checked Sep 16, 2026
11	Conosco	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	105 contacts →
	Indirect evidence “Cybersecurity specialists providing technology and telecoms solutions that gives you the leadership, experience and resilience you need to build and secure the future of work.” Source: RevenueBase Database · checked Sep 16, 2026
12	Caretower An Integrity360 Company	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	201-500	97 contacts →
	Indirect evidence “As an independent IT security specialist, Caretower provide comprehensive solutions to individual problems, thus allowing our recommendations to be unbiased.” Source: RevenueBase Database · checked Sep 16, 2026
13	ITC Secure	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	87 contacts →
	Indirect evidence “ITC Secure is an advisory-led cyber security services company.” Source: RevenueBase Database · checked Sep 16, 2026
14	Servoca Secure Solutions Limited	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	85 contacts →
	Indirect evidence “At Servoca Secure Solutions, we take great pride in delivering a multi-service security business; offering a range of complementary products and services to both the public and…” Source: RevenueBase Database · checked Sep 16, 2026
15	City Security Services Part Of City Group Security	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	201-500	64 contacts →
	Indirect evidence “City Security Services (CSS) have more than 25 years’ experience within the corporate security, public sector, education and social housing markets delivering manned guarding…” Source: RevenueBase Database · checked Sep 16, 2026
16	Cyro Cyber	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	62 contacts →
	Indirect evidence “Cyro Cyber are your cyber security Guardians.” Source: RevenueBase Database · checked Sep 16, 2026
17	Daintta	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	60 contacts →
	Indirect evidence “We provide deep expertise with technical and business specialists to help clients secure and protect the UK.” Source: RevenueBase Database · checked Sep 16, 2026
18	Assist Security Group	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	11-50	58 contacts →
	Indirect evidence “Assist Security Group (ASG) helps clients build resilient, comprehensive security strategies that protect their people and assets, business continuity and reputation.” Source: RevenueBase Database · checked Sep 16, 2026
19	Black Diamond Security	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	201-500	58 contacts →
	Indirect evidence “Black Diamond Security - Safeguarding Your World.” Source: RevenueBase Database · checked Sep 16, 2026
20	Cyberowl	Strong evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	52 contacts →
	Strong evidence “CyberOwl helps asset operators in the maritime and critical national infrastructure sectors gain visibility, cyber security and cyber compliance of systems on their distributed…” Source: RevenueBase Database · checked Sep 16, 2026
21	Hexegic	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	52 contacts →
	Indirect evidence “At Hexegic we are not just passionate about protecting data through our Cyber services we are passionate about helping companies release the potential of the data they hold…” Source: RevenueBase Database · checked Sep 16, 2026
22	Custom Intelligent Security	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	51 contacts →
	Indirect evidence “Established in Custom Intelligent Security is a technology driven ISO27001 & NSi Gold Accredited independent electronic security specialist with a proven track record of…” Source: RevenueBase Database · checked Sep 16, 2026
23	GSA Global	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	11-50	49 contacts →
	Indirect evidence “GSA Global helps organisations, families and individuals respond to serious, complex and emerging security risks.” Source: RevenueBase Database · checked Sep 16, 2026
24	Electranet UK Limited	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	49 contacts →
	Indirect evidence “Electranet’s mission is to be a preferred partner to the public and private sectors, bringing competitively priced, secure and innovative solutions to the market.” Source: RevenueBase Database · checked Sep 16, 2026
25	Frankton Group LTD	Indirect evidence	London, United KingdomHQ checked Sep 16, 2026	51-200	48 contacts →
	Indirect evidence “In today’s complex threat environment, businesses, individuals, and organisations require trusted partners to provide the ultimate assurance that their assets are well protected.” Source: RevenueBase Database · checked Sep 16, 2026

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 555 critical infrastructure defense based in London, United Kingdom

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Critical infrastructure defense based in London, United Kingdom at a glance

As of Sep 16, 2026

2.8%Verified-email coverage

160.9Average contacts per company

11-50Median size (employees)

100.0%Largest-city concentration · London

Sep 16, 2026Page data refreshed

Companies by employee count

1-10

258

11-50

183

51-200

201-500

501-1,000

1,001-5,000

5,001-10,000

10001+

Email recency for this list is measured across the whole United Kingdom list rather than for London, so it is reported there. Company counts and contact totals on this page are exact for London, over 555 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 London, 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 London 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, 2,507 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 in the United Kingdom

Critical infrastructure defense in London555
Critical infrastructure defense in Manchester49
Critical infrastructure defense in Birmingham36

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 London, United Kingdom?

RevenueBase identified 555 critical infrastructure defense headquartered in London, 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 2,507 verified decision-maker contacts tracked across these 555 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.

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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.