Company lists · Data verified August 2026

Top 25 Application security testing companies based in the United Kingdom

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

Compiled by the RevenueBase Data Team Verified Aug 28, 2026 322 companies tracked

There are 322 application security testing companies headquartered in the United Kingdom (RevenueBase, August 2026). RevenueBase tracks 4,132 professional contacts across them, including 962 with verified work emails and 358 with mobile numbers. London is the largest hub.

This list covers application security testing 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. Data current as of August 28, 2026.

322Companies

4,132Contacts tracked

962Verified emails

358Mobile numbers

Unlock all 322 companies Free account · no credit card · 2 minutes

The 25 largest application security testing companies based in the United Kingdom

Ranked by team size

Top 25 of 322 application security testing companies based in the United Kingdom, ranked by team size, largest first. Data verified Aug 28, 2026. Click a count to unlock that company's people.
#	Company	HQ	Employees	Contacts	Verified emails
1	Resillion	Glasgow	501-1,000	387	203
2	Portswigger	Knutsford	51-200	261	89
3	Appcheck LTD	Leeds	51-200	97	64
4	CSA Cyber	Gloucester	51-200	68	31
5	Covertswarm	London	51-200	65	41
6	Coretech Security	Cheltenham	51-200	41	7
7	Omerta	Saffron Walden	51-200	38	15
8	Secarma LTD	Manchester	11-50	34	23
9	Notsosecure Training Part Of Claranet Cyber Security	London	1,001-5,000	33	26
10	Aristi	Birmingham	11-50	32	10
11	Salus Cyber	Cheltenham	11-50	31	18
12	Ssl247 A Sectigo Company	London	51-200	24	1
13	Secure Purple	London	11-50	20	2
14	th4ts3cur1ty.company	London	11-50	19	13
15	SE Labs	London	11-50	19	11
16	Halo I.S	Leeds	11-50	19	9
17	CST Limited Computer Security Technology	London	11-50	17	2
18	Assure Technical	Malvern	11-50	16	10
19	Datasixth Consulting	London	51-200	14	7
20	MODUX	Avon	11-50	14	7
21	Ruptura Infosecurity	Milton Keynes	11-50	12	7
22	Infosec Partners	Winchester	11-50	12	1
23	CYTAL	London	11-50	11	10
24	Samurai Digital Security Limited	Birmingham	11-50	11	6
25	Secure Impact	Headquarters	11-50	10	6

Showing 25 of 322 application security testing companies based in the United Kingdom

See the full list, filter by size, metro and specialty, and get verified emails and direct dials for all 962 reachable decision-makers.

Free account · no credit card

See all 322 companies

Application security testing companies based in the United Kingdom at a glance

As of Aug 28, 2026

1-10Median size (employees)

LondonLargest hub · 123 HQs

358Contacts with mobile numbers

5Emails re-verified in last 30 days

Companies by employee count

1-10

201

11-50

51-200

201-500

501-1,000

1,001-5,000

5,001-10,000

Application security testing companies by metro

Metro	Companies
Application security testing companies in London	123
Application security testing companies in Manchester	16
Application security testing companies in Birmingham	9
Application security testing companies in Cheltenham	7
Application security testing companies in Leeds	6
Application security testing companies in Cambridge	4
Application security testing companies in Milton Keynes	4

How this list was built

Source: The RevenueBase company graph: 21.3 million companies and 398.9 million professional contacts resolved from primary sources.
Inclusion: Companies whose own business descriptions match “application security testing companies”, with match quality audited by blind human judging, and headquartered in the United Kingdom.
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: Contact records re-verify on a rolling cadence; 5 contacts on this list were re-verified in the last 30 days.
Refresh: Lists are refreshed periodically as the underlying company graph is re-verified. Last verified Aug 28, 2026.

Frequently asked

How many application security testing companies are there based in the United Kingdom?

There are 322 application security testing companies headquartered in the United Kingdom as of August 2026 (RevenueBase).

What is the largest company on this list?

Resillion, headquartered in Glasgow, tops this list with the largest team on record.

Which city has the most application security testing companies?

London leads with 123 headquartered companies, followed by Manchester (16) and Birmingham (9).

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 962 verified decision-maker contacts tracked across these 322 companies.

How current is this list?

The list is refreshed periodically as the underlying company graph is re-verified. It was last verified on August 28, 2026.

Ready to reach these companies? Verified emails and direct dials for all 322 application security testing companies based in the United Kingdom. Start with a free account, no credit card.

Get the full list

Related lists

Application security testing companies by geography

Browse the directory

Browse: Companies home · All United Kingdom lists · All Application security testing companies lists · New lists

About this data

RevenueBase is a B2B contact data platform. Its company graph covers 21.3 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, the same data that powers RevenueBase's B2B data products and the free research portal.