Penetration Testing London — Find Vulnerabilities Before Attackers Do

You Cannot Protect What You Do Not Understand

Every business has vulnerabilities. The question is whether you find them through a controlled assessment or through an actual breach. In 2026, with ransomware attacks on UK mid-market firms continuing to rise and regulatory penalties increasing year on year, the cost of not testing far exceeds the cost of testing.

Penetration testing gives you an honest picture of where your defences stand. Not the theoretical picture from a compliance checklist, but the practical reality of what an attacker could achieve if they targeted your business today.

What Our Pen Tests Cover

Our penetration testing in London covers your entire attack surface. We start externally, testing everything visible from the internet: your website, email gateway, VPN endpoints, cloud services, and DNS configuration. We look for vulnerabilities that would let an attacker gain initial access to your environment.

Then we move internal. With a foothold on your network (simulating a compromised employee device or a successful phishing attack), we test how far an attacker could move. Can they escalate privileges? Reach sensitive file shares? Access financial systems? Extract client data? This internal testing reveals the gaps that matter most, because initial access is not the goal — what happens after is what determines the damage.

For web applications, we test beyond the OWASP Top 10. Injection flaws, authentication bypasses, insecure direct object references, and business logic vulnerabilities are all in scope. If your application handles financial data or client information, particularly for hedge funds and regulated firms, these tests are essential.

Beyond the Scanner

Automated vulnerability scanners have their place. We run them as part of every engagement. But scanners miss the things that human testers find: chained vulnerabilities where three low-severity issues combine into a critical attack path, logic flaws in application workflows, misconfigured trust relationships between systems, and social engineering vectors that no scanner can test.

Our testers spend time understanding your environment, thinking like an attacker, and finding the paths of least resistance. The findings feed directly into our managed detection and response service to strengthen your ongoing defences. That is the difference between a vulnerability assessment and a genuine penetration test.

Which Test Do You Actually Need?

“Penetration testing” covers several different exercises with very different costs and outcomes. Buying the wrong one is the most common and most expensive mistake we see.

Test type	What it answers	Typical duration	When you need it
External infrastructure	What can an attacker reach from the internet?	2–4 days	Annually; required for most cyber insurance
Internal infrastructure	How far do they get once inside?	3–5 days	Annually, or after any office/network change
Web application	Can our app be abused or its data extracted?	3–10 days	Before launch, then annually or after major releases
Cyber Essentials Plus	Do we pass the certification’s technical audit?	1–2 days	At certification and each renewal
Red team	Would we actually detect a determined attacker?	3–6 weeks	Once your controls are already mature
Vulnerability scan	What known CVEs are exposed?	Automated, continuous	Monthly — this is not a pen test

The last row is where most confusion lives. A scan is a useful hygiene control and it is not a penetration test. If a supplier quotes you a few hundred pounds for a “pen test”, you are almost certainly buying an automated scan with a cover page.

What Penetration Testing Costs in the UK

Pricing is driven by scope and tester-days, not by company size. Realistic 2026 UK market ranges:

• External infrastructure test (up to ~30 live IPs): £2,000–£4,500
• Internal infrastructure test (single site, ~100 hosts): £3,000–£6,500
• Web application test (one authenticated app): £4,000–£12,000 depending on complexity and user roles
• Cyber Essentials Plus technical audit: £1,500–£3,000, sampling-based
• Red team engagement: £25,000+

Retesting after remediation should be included. If it is quoted as an extra, factor it in — a test you cannot afford to retest is a test whose findings never get closed.

CREST, CHECK and What the Badges Mean

The accreditation landscape confuses buyers, and some suppliers lean on that.

• CREST — an industry body accrediting both companies and individual testers. The most widely recognised commercial standard in the UK, and what most cyber insurers and enterprise procurement teams look for.
• CHECK — an NCSC scheme, required specifically for testing UK government and public-sector systems. If you are not touching government systems, you do not need CHECK.
• OSCP / CREST CRT — individual tester certifications. Useful signals about the person doing the work, not about the firm.
• “ISO 27001 certified” as a pen test credential — a red flag. It means the supplier has an information security management system, not that they can test yours.

Our testing is CREST-aligned and scoped to the same methodology. Ask any supplier — including us — who specifically will run your test and what they hold.

How to Prepare for a Pen Test

Firms that prepare get materially more value from the same spend:

1. Decide what you are protecting. “Test everything” produces a shallow test of everything. “Prove an attacker cannot reach the client portfolio database” produces a useful one.
2. Do the obvious patching first. Paying a senior tester day-rate to discover you have unpatched servers is poor value. Fix the known issues, then test for the unknown ones.
3. Get written authorisation. Testing systems without documented sign-off from the asset owner is a legal problem. Cloud providers may need notification too.
4. Warn the right people, not everyone. Your IT lead needs to know. If you tell the whole company, you are testing an alerted organisation, which is not the scenario you are worried about.
5. Book the remediation window before the test. Findings without allocated engineering time become a report that ages in a drawer.
6. Agree the escalation path. If we find something critical on day one, who do we call, and at what hour?

After the Test: Closing the Loop

A penetration test’s value is realised entirely in remediation. We prioritise findings by exploitability and business impact rather than raw CVSS score — a medium-severity flaw on your client portal usually matters more than a high-severity one on an isolated print server.

Where a finding reflects a systemic gap rather than a single misconfiguration, we say so. Repeated privilege-escalation paths usually point at Active Directory design; repeated web findings usually point at a development process without security review. Fixing the individual finding without fixing the source guarantees it returns at the next test — which is why our testing findings feed into managed detection and response and, where the root cause is human, security awareness training.

Clear Reporting, Real Remediation

Every pen test produces two deliverables. The executive summary is a 2-3 page document your board and compliance team can read in 10 minutes. It covers the scope, key findings, overall risk posture, and strategic recommendations.

The technical report contains every finding with full details: what we found, how we exploited it, what an attacker could achieve, and exactly how to fix it. Remediation steps are specific and actionable — not generic advice like “apply patches” but precise instructions your IT team can follow.

After remediation, we re-test every finding to confirm the fix is effective. You receive an updated report showing the before and after state of each vulnerability.

Compliance and Regulation

For FCA-regulated firms, regular penetration testing satisfies requirements under DORA’s digital operational resilience testing framework. We scope our tests to align with regulatory expectations and produce reports formatted for submission to compliance and audit teams. Cyber Essentials Plus certification also requires an external vulnerability test, which our assessment covers.