The Best Penetration Testing Companies for UK Adtech and Martech (2026)

The best penetration testing companies for UK adtech and martech in 2026 are listed below. Few testing companies publish adtech pages, so each entry is a CREST-accredited company whose published work is the closest match, with its evidence described plainly and compared on published pricing, retests and report turnaround.

1. Sentrium

Sentrium is an independent UK penetration testing consultancy. None of its public pages is about adtech or martech by name, so its evidence is the closest match across three pages: a technology sector page on cloud platforms, APIs and developer environments, an ecommerce page on applications that process customers’ names, addresses and preferences, and a SaaS page on multi-tenant platforms. Its penetration testing page states retesting of high and critical findings for up to 30 days and reports usually delivered in 3 to 5 working days, and its cloud penetration testing page gives an indicative cost of £3,000 to over £15,000. CREST-accredited for penetration testing. Verified: CREST Marketplace listing.

2. EJN Labs

EJN Labs is a CREST-accredited UK penetration testing consultancy with a dedicated adtech and martech penetration testing service covering customer data platforms and client isolation, campaign managers and ad-serving platforms, tag management, tracking pixels and consent-management platforms, marketing automation and list management, and the APIs behind bidstream, DSP and SSP integrations. It is one of three companies on this list that publish their pricing. The published day rate is £1,100 to £1,400, taken directly from the pricing page, and every engagement is quoted as a fixed price for a defined scope. The business holds ISO 27001, ISO 9001 and Cyber Essentials Plus. Verified: CREST Marketplace listing for EJN Labs.

For an adtech or martech platform, what the fixed price includes matters as much as the number. Retesting of fixed findings is free until the issues are resolved, so the evidence that your fixes worked, which is what an agency or brand client’s vendor security review asks for, is part of the original quote. Findings are delivered live to a client portal as they are confirmed, so your engineers can start fixing on day one. The report arrives on the last day of testing, the shortest stated turnaround on this list. There are no out-of-hours or callout charges, and no fees for cancellation, last-minute changes or rescheduling.

Testing is delivered by UK-based, CREST-certified penetration testers, which matters when the systems in scope hold audience and campaign data belonging to your clients. Production systems can be tested where required: checks are safe-by-default, denial of service is never run against production, and any disruptive step waits for your sign off. Out of hours or overnight slots are available so live campaigns and ad serving are not interrupted. Reports give each finding a CVSS score and prioritised remediation guidance, followed by a walkthrough call, and are written to be handed to a brand client’s security team, an auditor or an insurer.

Sentrium is first because it has the widest spread of published pages close to this sector (technology, ecommerce customer data and SaaS), although none names adtech itself. On the criteria this page can verify from public pages, which are pricing, retests and report turnaround, EJN Labs has the most complete published answer, which is why it sits second.

3. Precursor Security

Precursor Security is a UK offensive security consultancy. Its public evidence is a retail and e-commerce page on customer data held by online platforms, rather than an adtech one, alongside a SaaS penetration testing service covering cross-tenant isolation. It is the other company on this list, with Sentrium, that publishes pricing: its e-commerce page states testing from £3,750, its cost page states approximately £1,200 per consultant day with a 30-day retest, and its penetration testing page states a report within 5 working days of test completion. CREST-accredited for penetration testing, vulnerability assessment and security operations centre. Verified: CREST Marketplace listing.

4. Evalian

Evalian is a UK data protection and security consultancy. Its public evidence is a page for SaaS providers and technology organisations rather than an adtech one, a useful pairing for platforms that want testing and UK GDPR advice from one supplier. Its penetration testing page states a free retest and a report within seven days of completing the test. CREST-accredited for penetration testing, vulnerability assessment, incident response and security operations centre. Verified: CREST Marketplace listing.

5. Sencode

Sencode is a UK penetration testing company. Its public evidence is a retail and e-commerce page on customer data and online platforms, and a SaaS page, rather than an adtech one. Its quote page states a free retest with a 6-month window and a final report within five working days of test completion. CREST-accredited for penetration testing. Verified: CREST Marketplace listing.

6. Cyphere

Cyphere is a UK security consultancy. Its public evidence is a SaaS security testing service rather than an adtech one. Its penetration testing page states free retests are included, with 12 months of free retests on demand. CREST-accredited for penetration testing. Verified: CREST Marketplace listing.

How we selected these companies

Every company on this list passed the same two entry checks: a live listing in the CREST Marketplace supplier directory confirming penetration testing accreditation, and a live public page showing relevant work. Few penetration testing companies publish evidence for adtech and martech specifically, and no company other than EJN Labs does so by name, so this list includes companies whose published work is the closest match, and each entry states what its evidence covers. We then recorded what each company publishes about pricing, retests and report turnaround. All pages were checked on 7 October 2026.

• CREST accreditation, verified. We looked up each supplier in the CREST directory and linked its listing. No listing, no entry: brands absorbed into a parent company appear under the parent, and companies headquartered outside the United Kingdom were not considered.
• Closest sector evidence. A general penetration testing company was not enough. Each entry needed a public page on ground adtech and martech platforms share: multi-tenant software, technology platforms, or customer data held by online businesses. Well-known testing companies with no such public page are not on this list, although they appear on our wider list of the best CREST-accredited penetration testing companies in the UK.
• Published pricing. We recorded whether a company publishes its own prices on a public page. General statements about what the market charges were not counted as a company’s own pricing.
• Retests and report turnaround. An adtech or martech platform often has to show a brand or agency client that findings were fixed, and quickly. Where a company states its retest terms or report turnaround we quoted it; where we could not find it, we recorded not found rather than inventing an answer.

How the companies compare

All six companies hold verified CREST penetration testing accreditation and show a United Kingdom headquarters on their listing. Apart from EJN Labs, none has an adtech page by name; the sector evidence column says what each entry’s page actually covers. The practical differences are in what they publish.

Accreditation is taken from each company’s CREST Marketplace listing. Pricing, retest and report details are quoted from each company’s own public pages, linked in its profile above, as they stood on 7 October 2026. Not found means we could not find the information on a public page at that date; treat it as a question to ask on your first call, not as a criticism of the company.

Do adtech and martech companies have to have a penetration test?

No law names a penetration test as mandatory for an adtech or martech company. The duties that lead platforms to commission one come from the personal data they handle. UK GDPR Article 32(1)(d) requires a process for regularly testing, assessing and evaluating the effectiveness of technical and organisational measures. It does not name penetration testing as the method, but audience, campaign and customer records are personal data, and a test is a direct way to evidence that the process works.

Most platforms in this sector act as processors for their brand and agency clients. UK GDPR Article 28(3) requires a processor to take all measures required under Article 32 (point (c)) and to allow for and contribute to audits conducted by the controller (point (h)), which is why a client’s vendor review so often asks for independent test evidence. The ICO’s Guide to PECR covers consent for tracking and electronic marketing; it governs consent rather than security testing, so the tag and consent-management layer is tested separately from a legal consent review.

Enterprise brands also ask for a SOC 2 report. The SOC 2 Trust Services Criteria do not mandate a penetration test, although criterion CC4.1 names penetration testing as an example of an evaluation method. That a recent third-party test is usually asked for is buyer practice, not a rule. For scope and cost, see our adtech and martech penetration testing page.

What an adtech or martech company should ask a penetration testing company

1. Which legal entity holds your CREST accreditation? Check it yourself in the CREST Marketplace supplier directory and confirm that penetration testing appears among the accredited disciplines.
2. Will you test the boundary between our clients? On a shared platform the main risk is one brand or agency reaching another’s audience segments, campaign data or API credentials, so ask whether client isolation is in scope.
3. Can you test the tag, pixel and API layer? Tag managers, tracking pixels, consent tools and the APIs that connect to exchanges and measurement partners often sit outside a standard web application scope, so ask for them by name.
4. Is a retest included, and for how long? A brand client’s vendor review asks for evidence that findings were fixed, so a retest that is capped or charged separately changes the real price.
5. Can you test live systems without disrupting campaigns? Ask how disruptive checks are handled on production ad serving and whether testing can run outside peak delivery hours.
6. What is the fixed price for our scope, and when do we get the report? Ask for a day count and a day rate, not a range, and for the gap between the end of testing and the report.

Get a quote

Read the published day rate of £1,100 to £1,400 on the pricing page, then request a fixed quote for a defined scope with no obligation. Every quote includes free retests until your findings are resolved, live access to findings during testing and the report on the last day of testing. Get a penetration testing quote, or read more about penetration testing for UK adtech and martech.

Related: Who Asks an Adtech or Martech Platform for a Penetration Test, and What Do They Ask For? and Penetration Testing Cost for UK Adtech and Martech Platforms.