The Best Penetration Testing Companies for UK Accountancy and Professional Services Firms (2026)

The best penetration testing companies for UK accountancy and professional services firms in 2026 are listed below. Each one holds a verified CREST penetration testing accreditation and shows public evidence of working with accountancy practices or professional services firms, and each is compared on published pricing, retests and report turnaround.

1. Mitigo

Mitigo is a UK cyber risk management company that works in partnership with the Institute of Chartered Accountants in England and Wales, the Institute of Chartered Accountants of Scotland and CharterGroup, as stated on its cyber security for accountants page. It is listed among ICAEW member offers, where its technology assessments are described as including penetration testing. It is 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 accountancy and professional services penetration testing service for practices, auditors, tax advisers and consulting firms, covering client portals, tax upload, audit data rooms and practice management platforms. It is the only company on this list that publishes its 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 accountancy practice, 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 audit client, a corporate customer’s security questionnaire or a cyber insurer usually asks for, is part of the original quote. Findings are delivered live to a client portal as they are confirmed, so your IT team or managed provider can start fixing on day one. The report arrives on the last day of testing, the only 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 client tax records, payroll data and audit working papers. 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 staff are not interrupted during filing deadlines. Reports give each finding a CVSS score and prioritised remediation guidance, followed by a walkthrough call, and are written to be handed to a client, an insurer or an auditor.

Mitigo’s partnerships with the professional bodies keep it first. 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. NCC Group

NCC Group is a UK-headquartered global cyber security company. Its legal and professional services page lists penetration testing for law firms, audit agencies, consultancies, estate agencies, accountancies and other professional services. Its CREST listing shows accreditation for penetration testing, vulnerability assessment, incident response and security operations centre, among others. Verified: CREST Marketplace listing.

4. WorkNest Cyber (incorporating Pentest People and Bulletproof)

WorkNest is a UK business group whose cyber security arm combines Bulletproof, Target Defence and Pentest People. Its professional services cyber security page describes the client data and financial records that professional services firms must protect. The CREST listing is held under the combined WorkNest Cyber name and shows accreditation for penetration testing, vulnerability assessment, incident response, application security testing and mobile application security testing. Verified: CREST Marketplace listing for WorkNest Cyber.

5. Prism Infosec

Prism Infosec is a UK cyber security consultancy with a cyber security for professional services page that covers securing the cloud platforms professional firms use for collaboration and data storage. It is CREST-accredited for penetration testing, vulnerability assessment, incident response, incident exercising and threat led penetration testing. Verified: CREST Marketplace listing.

6. Integrity360

Integrity360 is a European cyber security company that lists a London office and shows an Irish headquarters on its CREST listing. Its professional services page describes serving professional services firms, and its cybersecurity testing services include penetration testing. CREST-accredited for penetration testing and incident response. 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 public evidence of work with accountancy or professional services firms. 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.
• Accountancy and professional services evidence. A general penetration testing company was not enough, and a page about law firms alone did not count. Each entry needed a public page showing accountancy or professional services work: a professional body partnership or listing, or a dedicated professional services page. 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 accountancy firm usually has to show clients and insurers that findings were fixed, often before a renewal date. 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 have public accountancy or professional services evidence. Every one shows a United Kingdom headquarters on its listing except Integrity360, which shows Ireland. 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 accountancy and professional services firms have to have a penetration test?

No rule we found names a penetration test as mandatory for an accountancy practice or professional services firm. The duties that lead firms to commission one are broader. Regulation 8(2)(c) of the Money Laundering Regulations 2017 brings auditors, insolvency practitioners, external accountants and tax advisers within the regulations, and HMRC guidance explains who needs to register for money laundering supervision. Those are anti-money-laundering duties and do not name a security test, but they mean a practice holds identity documents and client financial records that an attacker would value.

UK GDPR Article 32(1)(d) requires a process for regularly testing the effectiveness of your security measures. It does not name penetration testing as the method, but a test is one recognised way to evidence that process for client tax records, payroll data and audit working papers. In practice the request usually comes from outside the firm: a corporate client’s supplier questionnaire, an audit client, or a cyber insurer’s proposal form, where requirements vary by insurer and policy. For the wider picture, see our guide to where penetration testing fits ICAEW cyber guidance and our GDPR penetration testing page.

What an accountancy or professional services firm 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. Where are the testers based, and who will see our data? Client tax records, payroll files and audit working papers may be visible during testing, so ask where the people doing the work are located and how findings are stored.
3. Will you test the client portal and tax upload paths, not just the website? Ask how access between one client’s files and another’s is checked.
4. Is a retest included, and for how long? Audit clients and insurers ask for evidence that findings were fixed, so a retest that is capped or charged separately changes the real price.
5. When do we get the report, and can you test around filing deadlines? Ask about out of hours testing and how disruptive checks are handled on live systems.
6. What is the fixed price for our scope? Ask for a day count and a day rate, not a range.

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 accountancy and professional services firms.

Related: Client Due Diligence: Does Your Accountancy Firm Need a Penetration Test? and Penetration Testing Cost for UK Accountancy and Professional Services Firms.