Company lists · Data refreshed September 2026

Top 25 Appsec companies based in the United Kingdom

Name: Appsec companies based in the United Kingdom
Creator: RevenueBase
License: https://creativecommons.org/licenses/by/4.0/

Compiled by the RevenueBase Data Team Data refreshed Sep 21, 2026 900 companies tracked

RevenueBase identified 900 appsec companies headquartered in the United Kingdom as of September 2026 and tracks 9,896 professional contacts across them, including 2,971 with verified work emails. London is the largest hub.

This list covers appsec companies 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 21, 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 21, 2026 86% judged on-target in blind review

900Companies

9,896Contacts tracked

2,971Verified emails

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The 25 largest appsec companies based in the United Kingdom

Ranked by team size

Top 25 of 900 appsec companies based in the United Kingdom, ranked by team size, largest first. Data refreshed Sep 21, 2026. RevenueBase Smart Search rates how each company's information relates to appsec companies: 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	COBRA	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	n/a	705 contacts →
	Indirect evidence “Get a free, powerful security assessment with personalised recommendations, the same analysis that costs from IT Consultancies.” Source: RevenueBase Database · checked Sep 21, 2026
2	Securityhq	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	501-1,000	502 contacts →
	Indirect evidence “SecurityHQ, a global cybersecurity company pioneering Security Performance Engineering for stronger operational performance and resilience.” Source: RevenueBase Database · checked Sep 21, 2026
3	Quorum Cyber	Indirect evidence	Edinburgh, United KingdomHQ checked Sep 21, 2026	201-500	297 contacts →
	Indirect evidence “At Quorum Cyber, we're on a mission to help good people win.” Source: RevenueBase Database · checked Sep 21, 2026
4	Portswigger	Indirect evidence	Knutsford, United KingdomHQ checked Sep 21, 2026	51-200	267 contacts →
	Indirect evidence “PortSwigger is a global leader in the creation of software tools for security testing of web applications.” Source: RevenueBase Database · checked Sep 21, 2026
5	Turnkey Consulting	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	51-200	134 contacts →
	Indirect evidence “Turnkey Consulting brings together people, protection, and performance to help the world’s leading companies understand and optimize their risk and security landscape.” Source: RevenueBase Database · checked Sep 21, 2026
6	Bulletproof Cyber Security	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	51-200	123 contacts →
	Indirect evidence “Bulletproof is now part of WorkNest Secure.” Source: RevenueBase Database · checked Sep 21, 2026
7	Appcheck LTD	Indirect evidence	Leeds, United KingdomHQ checked Sep 21, 2026	51-200	99 contacts →
	Indirect evidence “AppCheck is a Complete Enterprise Security Testing Solution that provides up to the minute vulnerability coverage for your entire estate.” Source: RevenueBase Database · checked Sep 21, 2026
8	Caretower An Integrity360 Company	Indirect evidence	London, United KingdomHQ checked Sep 21, 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 21, 2026
9	Cognisys	Indirect evidence	Leeds, United KingdomHQ checked Sep 21, 2026	51-200	90 contacts →
	Indirect evidence “Solutions \| Testing \| Knowledge Helping You Protect Your Business From Cyber Attackers Your security and compliance partner, delivering trust worldwide Cognisys are your trusted…” Source: RevenueBase Database · checked Sep 21, 2026
10	Titania LTD	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	51-200	88 contacts →
	Indirect evidence “Dedicated to securing the networks society depends on.” Source: RevenueBase Database · checked Sep 21, 2026
11	Foregenix	Indirect evidence	Swindon, United KingdomHQ checked Sep 21, 2026	51-200	80 contacts →
	Indirect evidence “When your business relies on security, compliance and a strong reputation for taking care of your customers, you need a partner that understands your ethos, your challenges and…” Source: RevenueBase Database · checked Sep 21, 2026
12	White HAT An Epam Company	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	51-200	77 contacts →
	Indirect evidence “White Hat, part of the EPAM group, is an award-winning cyber intelligence and offensive security company that leverages an attacker’s perspective to shape innovative, proactive…” Source: RevenueBase Database · checked Sep 21, 2026
13	Dionach By Nomios	Indirect evidence	Oxford, United KingdomHQ checked Sep 21, 2026	51-200	73 contacts →
	Indirect evidence “Dionach by Nomios has over 25 years of expertise in information security, supporting organisations in building resilience against ever‑evolving cyber threats.” Source: RevenueBase Database · checked Sep 21, 2026
14	CSA Cyber	Indirect evidence	Gloucester, United KingdomHQ checked Sep 21, 2026	51-200	69 contacts →
	Indirect evidence “Modern cyber resilience demands more than isolated controls.” Source: RevenueBase Database · checked Sep 21, 2026
15	Telesoft	Indirect evidence	Blandford, United KingdomHQ checked Sep 21, 2026	51-200	68 contacts →
	Indirect evidence “The organisations that run our world face relentless complexity and evolving threats.” Source: RevenueBase Database · checked Sep 21, 2026
16	Interrupt Labs	Indirect evidence	Basingstoke, United KingdomHQ checked Sep 21, 2026	51-200	65 contacts →
	Indirect evidence “We’re here to provide world-leading vulnerability research and capabilities!” Source: RevenueBase Database · checked Sep 21, 2026
17	Covertswarm	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	51-200	64 contacts →
	Indirect evidence “YOU DESERVE TO BE HACKED®.” Source: RevenueBase Database · checked Sep 21, 2026
18	Digitalxraid	Indirect evidence	Doncaster, United KingdomHQ checked Sep 21, 2026	51-200	62 contacts →
	Indirect evidence “At DigitalXRAID, we’re more than just a managed security services provider – we’re your trusted partner in safeguarding your business from cyber threats.” Source: RevenueBase Database · checked Sep 21, 2026
19	Intruder	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	51-200	61 contacts →
	Indirect evidence “Intruder's continuous exposure management platform helps security, IT, and engineering teams stop breaches before they start.” Source: RevenueBase Database · checked Sep 21, 2026
20	MDSEC	Indirect evidence	Macclesfield, United KingdomHQ checked Sep 21, 2026	11-50	61 contacts →
	Indirect evidence “MDSec are a UK based consultancy with a passion for information security.” Source: RevenueBase Database · checked Sep 21, 2026
21	Threatspike	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	51-200	61 contacts →
	Indirect evidence “ThreatSpike is the world's first AI-managed IT and security platform, replacing the legacy MSP model entirely.” Source: RevenueBase Database · checked Sep 21, 2026
22	Garrison NOW A Part Of Everfox	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	51-200	60 contacts →
	Indirect evidence “Garrison is a London-based cybersecurity company founded in 2014 by David Garfield (CEO) and Henry Harrison (Chief Scientist).” Source: RevenueBase Database · checked Sep 21, 2026
23	NEXOR	Indirect evidence	Nottingham, United KingdomHQ checked Sep 21, 2026	51-200	59 contacts →
	Indirect evidence “Nexor is a Secure Information Exchange Specialist offering High Assurance threat and risk mitigation expertise and solutions into complex and sensitive networks globally.” Source: RevenueBase Database · checked Sep 21, 2026
24	Cyberlab	Indirect evidence	Alderley Edge, United KingdomHQ checked Sep 21, 2026	51-200	57 contacts →
	Indirect evidence “CyberLab is the UK-leading cyber security consultancy and managed services provider, trusted by over 1,200 enterprise businesses, government departments, and household names to…” Source: RevenueBase Database · checked Sep 21, 2026
25	Secureflag	Indirect evidence	London, United KingdomHQ checked Sep 21, 2026	51-200	57 contacts →
	Indirect evidence Source: RevenueBase Database · checked Sep 21, 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: appsec companies. 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 appsec companies.
Partial evidence: Its own public description names part of appsec companies, so it works in or next to the category without describing itself that way.
Indirect evidence: The description shown does not name appsec companies. 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 900 appsec companies based in the United Kingdom

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Appsec companies based in the United Kingdom at a glance

As of Sep 21, 2026

30.0%Verified-email coverage

11.0Average contacts per company

1-10Median size (employees)

42.2%Largest-city concentration · London

Sep 21, 2026Page data refreshed

Companies by employee count

1-10

570

11-50

253

51-200

201-500

501-1,000

1,001-5,000

5,001-10,000

10001+

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 900 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 appsec companies, 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 “appsec companies”. 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 appsec companies), 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 appsec companies, 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, 2,971 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 21, 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.

Appsec companies by metro

Appsec companies in London380
Appsec companies in Manchester39

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 appsec companies, 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 appsec companies are there based in the United Kingdom?

RevenueBase identified 900 appsec companies 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?

COBRA, headquartered in London, tops this list with the largest team on record.

Which city has the most appsec companies?

London leads with 380 headquartered companies, followed by Manchester (39) and Birmingham (18).

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 2,971 verified decision-maker contacts tracked across these 900 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 21, 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.