The verdict in three sentences
Securing a web app for a London company in 2026 means a penetration test at 5,000 – 20,000 EUR, a GDPR audit (records, DPA, EU data residency) and remediation scaled to findings. Plan for 3 to 6 weeks depending on scope. The investment is trivial against the cost of a customer-data breach or a blocked payment flow.
Security and compliance: two linked workstreams
Security and GDPR compliance reinforce each other but are not the same. Security answers "does my app withstand attacks?" (injection, authentication, session handling, vulnerable dependencies — the OWASP framework). Compliance answers "am I allowed to process this data and how do I protect it?" (consent, minimization, retention, data-subject rights).
As soon as an app handles customer data and payments, both are mandatory. Under UK GDPR and EU GDPR, you also need to control data residency and sign Data Processing Agreements (DPA) with your processors.
Cost of security services (2026, order of magnitude)
| Service | Scope | Cost (EUR) | Timeline |
|---|---|---|---|
| Security audit | Code, config review, OWASP Top 10 | 4,000 – 12,000 | 1 – 3 wks |
| Penetration test | Controlled attack, exploitation | 5,000 – 20,000 | 2 – 4 wks |
| GDPR compliance | Records, notices, consent, DPA | 3,000 – 12,000 | 2 – 4 wks |
| Remediation | Depending on findings | 4,000 – 25,000 | 2 – 6 wks |
| Monitoring & maintenance | Continuous surveillance | 400 – 1,800 /month | ongoing |
The remediation line varies widely: a healthy app costs little to fix, while an app with critical flaws needs a real remediation effort.
Risk levels and priorities
| Risk level | Example | Priority | Typical fix cost (EUR) |
|---|---|---|---|
| Critical | Injection, exposed data | Immediate | 6,000 – 25,000 |
| High | Weak auth, insecure session | < 2 weeks | 3,000 – 12,000 |
| Medium | Outdated dependencies | < 1 month | 1,500 – 6,000 |
| Low | Missing headers, config | Scheduled | 600 – 2,500 |
A good engagement does not just list flaws: it ranks them by real risk and proposes a priced remediation plan. That turns a report into actionable decisions.
Mini case study
Aisha, technical lead of a B2B services platform in London, handles data for 12,000 customers and processes card and mobile payments. Ahead of a funding round, an investor demands proof of security. She commissions an audit + pentest at 19,000 EUR revealing 2 critical and 5 medium flaws. Remediation costs 9,500 EUR, a total of 28,500 EUR. Against the risk: a breach across 12,000 customers could trigger fines, lost trust and a failed round — a potential cost far above 60,000 EUR. The investment protects both customers and valuation.
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FAQ
How much does a security audit cost from London in 2026?
A security audit costs 4,000 to 12,000 EUR depending on app size. A penetration test (controlled attack) adds 5,000 to 20,000 EUR.
What is the difference between an audit and a pentest?
The audit reviews code and configuration against OWASP; the pentest simulates a real attack to exploit flaws. They are complementary: the audit finds broadly, the pentest proves exploitability.
Do I need EU data residency and a DPA?
Under UK/EU GDPR, if you process EU residents' data you must control data residency and sign DPAs with processors. A GDPR compliance engagement costs 3,000 to 12,000 EUR.
How long does full hardening take?
Usually 3 to 6 weeks: a few weeks of audit and pentest, then remediation scaled to the severity of findings.
Is monitoring needed after fixes?
Yes. Security is not a fixed state: monitoring at 400 – 1,800 EUR/month watches for new vulnerabilities and intrusion attempts continuously.
Let's scope your project. Describe your app (customer data, payments, stack) and your deadline (funding round, compliance); we'll frame audit, pentest and remediation. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.
Mohamed Bah
Fondateur, Kolonell
Passionate about digital and entrepreneurship in Africa, Mohamed has been helping Sénégalese businesses with their digital transformation since 2020. Founder of Kolonell, he believes every SME deserves a professional and accessible online présence.
