nhs-synthetic-data

name	nhs-synthetic-data
description	Use when generating synthetic NHS test data including NHS numbers, patient names, SNOMED codes, and seed scripts for development and demos.

NHS Synthetic Data — Test Data Generation

This skill generates realistic but entirely synthetic test data for NHS digital services. Real patient data must never be used in development, testing, or demos — this is a UK GDPR and NHS policy requirement.

When to Use

• Creating seed data for local development databases
• Writing test fixtures for pytest or Vitest
• Building demo datasets for stakeholder presentations
• Generating realistic form submissions for E2E tests
• Populating prototype screens with example data

NHS Number Generation

NHS numbers are 10 digits with a Modulus 11 check digit. The algorithm:

1. Multiply each of the first 9 digits by (11 - position), where position is 1-indexed
2. Sum the products
3. Remainder = sum mod 11
4. Check digit = 11 - remainder
5. If check digit is 11, use 0. If check digit is 10, the number is invalid — regenerate

Implement generate, format (3-3-4 with spaces), and validate functions in the backend language from tech-stack.instructions.md.

Pre-validated Synthetic NHS Numbers

These numbers pass the Modulus 11 check and are designated for testing:

NHS Number	Formatted	Use Case
9434765919	943 476 5919	Default test patient
9000000009	900 000 0009	Boundary test
9111111124	911 111 1124	Second test patient
9222222228	922 222 2228	Third test patient
9876543210	987 654 3210	Demo presentations

Synthetic Patient Data

Patient Records

Use these synthetic personas consistently across the service:

NHS Number	Given Name	Family Name	DOB	Postcode	GP Surgery	Gender
943 476 5919	Sarah	Thompson	1991-03-15	LS1 4AP	Kirkstall Health Centre	female
911 111 1124	James	Wilson	1954-08-22	M1 2WD	Manchester Medical Practice	male
922 222 2228	Priya	Patel	1985-11-30	B1 1BB	City Centre Surgery	female
987 654 3210	David	Roberts	1968-06-10	SW1A 1AA	Westminster Health Practice	male
900 000 0009	Fatima	Khan	2000-01-25	LS2 9JT	University Health Service	female

Synthetic Appointments

Patient NHS Number	Date	Time	Type	Clinician	Location	Status
943 476 5919	2026-03-15	09:30	GP appointment	Dr. Ahmed	Kirkstall Health Centre	booked
943 476 5919	2026-03-22	14:00	Blood test	Nurse Williams	Kirkstall Health Centre	booked
911 111 1124	2026-03-10	10:15	Annual health check	Dr. Chen	Manchester Medical Practice	completed

Synthetic Clinical Codes (SNOMED CT)

Use real SNOMED CT concept IDs with synthetic patient associations:

SNOMED Code	Display Term	Common Use
38341003	High blood pressure (hypertension)	Long-term condition
73211009	Diabetes mellitus (diabetes)	Long-term condition
195967001	Asthma	Long-term condition
386661006	Fever	Symptom
25064002	Headache	Symptom
267036007	Shortness of breath	Symptom
182531007	Paracetamol (medication)	Prescription
318475005	Amoxicillin (medication)	Prescription

Test Fixtures

Create test fixtures from the patient and appointment data above, using the test framework from tech-stack.instructions.md. Provide both single-patient and all-patients fixtures for unit and integration tests respectively.

Rules

• Never use real NHS numbers — always generate with the Modulus 11 algorithm or use the pre-validated list
• Never use real patient names — use the synthetic personas defined above
• Never use real postcodes linked to real people — use well-known institutional postcodes
• Synthetic data must be clearly labelled — add comments marking data as synthetic in seed scripts
• NHS number display — always format as 3-3-4 with spaces: 943 476 5919
• Dates — use future dates for appointments, past dates for historical records
• Consistency — use the same synthetic patients across all tests and demos for a coherent narrative

References

• NHS Number Format
• NHS Number Modulus 11 Check
• SNOMED CT Browser
• NHS Synthetic Data Guidance