The verdict in three sentences
For a London vendor serving 40 business customers, the multi-tenant model you choose drives your cloud bill, your security posture and your ability to pass buyers' due diligence. A shared database with row-level security (RLS) fits most customers, and a dedicated database is reserved for the 3 to 5 accounts that require it by contract. Budget GBP 60,000 to 150,000 for design and build, for infrastructure of GBP 500 to 2,200 a month.
The three isolation models compared
The CTO has to choose between three architectures. A shared database puts every customer in the same tables, with a tenant_id column and PostgreSQL RLS policies that technically prevent a query from reading another customer's data. Schema per tenant creates a separate namespace inside one database. Database per tenant gives each account its own server or cluster.
| Criterion | Shared database with RLS | Schema per tenant | Database per tenant |
|---|---|---|---|
| Data isolation | Logical, strong if RLS is tested | Stronger logical | Physical |
| Infra cost for 40 customers | GBP 500 to 800 a month | GBP 800 to 1,200 a month | GBP 1,600 to 2,200 a month |
| Onboarding a new customer | Seconds | Minutes | 30 to 60 automated minutes |
| Schema migrations | One | 40 to orchestrate | 40 to orchestrate |
| Per-customer backup and restore | Complex | Medium | Simple |
| Security questionnaire answers | Needs explaining | Well accepted | Very well accepted |
A hybrid model often wins: shared database for 35 customers, dedicated databases sold as a premium option to large accounts, on the same application code.
2026 budget for a London vendor
The figures below cover designing or rebuilding the multi-tenant layer of an existing product, not a full rewrite.
| Item | Shared RLS | Hybrid model | Database per tenant |
|---|---|---|---|
| Current-state audit and target model | GBP 6,000 | GBP 9,000 | GBP 10,000 |
| Tenant layer, RLS and request context | GBP 19,000 | GBP 25,000 | GBP 25,000 |
| Database routing and provisioning | GBP 4,000 | GBP 18,000 | GBP 37,000 |
| Orchestrated migrations and CI | GBP 7,500 | GBP 14,000 | GBP 25,000 |
| Encryption, key management, logging | GBP 9,000 | GBP 13,000 | GBP 17,000 |
| Isolation tests and penetration test | GBP 7,500 | GBP 11,000 | GBP 15,000 |
| UK GDPR documentation and contract annexes | GBP 7,000 | GBP 10,000 | GBP 21,000 |
| Indicative total | GBP 60,000 | GBP 100,000 | GBP 150,000 |
These are 2026 ballpark figures. Infrastructure usually runs on AWS, Azure or Google Cloud in the London region, with an EU region added for continental customers.
What your enterprise customers will demand
A UK or European enterprise buyer sends a security questionnaire of 80 to 250 questions before signing. The blocking items always return: UK or EU data residency, a data processing agreement compliant with Article 28 of UK GDPR, a sub-processor list, encryption at rest and in transit, restore time objectives, and breach notification within 72 hours. Many also ask for ISO 27001 or Cyber Essentials Plus. An architecture that logs every access per tenant makes these answers far easier and shortens procurement by several weeks.
Mini case study
Priya, CTO of an HR software vendor in Shoreditch, serves 40 customers in the UK and the Netherlands and loses tenders for lack of demonstrable isolation. She picks the hybrid model at GBP 100,000: 36 customers on shared RLS, 4 on dedicated databases.
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The math: infrastructure drops from 40 small legacy instances (about GBP 2,500 a month) to GBP 1,150 a month, saving GBP 16,200 a year. The 4 dedicated databases are billed at GBP 220 a month each, i.e. GBP 10,560 a year of extra revenue. With one new enterprise contract at GBP 45,000 a year won on the strength of the security pack, the project pays back in under 18 months.
FAQ
Is row-level security enough for HR or health data?
For HR data, yes, provided isolation is tested automatically on every deployment. For NHS-related health data, the DSPT and buyer requirements often push towards a dedicated database.
Can we switch models later?
Yes, if the code uses a single tenant context from the start. Moving one customer from the shared database to a dedicated one then takes 1 to 2 days instead of several weeks.
How many engineers does the architecture need?
One half-time platform engineer is enough up to about 150 customers, if migrations and provisioning are automated in CI.
Should we host in the UK or the EU?
Both, often: London for UK customers and Frankfurt or Dublin for EU customers. The UK holds an EU adequacy decision, but many continental buyers still require EU residency in their DPA.
What timeline should we plan?
Plan 10 to 14 weeks for a shared RLS model and 16 to 24 weeks for a hybrid or per-tenant model, including migration of the 40 customers.
Let's scope your project. Share your customer count, stack and contractual requirements: we will price the architecture between GBP 60,000 and 150,000, with a 10 to 24 week plan. 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.
