UK National Insurance Number Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching uk national insurance number, ported and verified for Python. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# UK National Insurance Number
# ReDoS-safe | RegexVault — Finance > Tax & Registration

import re

uk_national_insurance_number_pattern = re.compile(r'^(?:QQ|(?!BG|GB|NK|KN|TN|NT|ZZ)[A-CEGHJ-NOPR-TW-Z]{1}[A-CEGHJ-NPR-TW-Z]{1})[0-9]{6}[A-D]$')

def validate_uk_national_insurance_number(value: str) -> bool:
    return bool(uk_national_insurance_number_pattern.fullmatch(value))

# Example
print(validate_uk_national_insurance_number("AB123456C"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Tax & Registration category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

Invalid prefixes: BG, GB, NK, KN, TN, NT, ZZ. Second letter excludes D, F, I, Q, U, V. First letter also excludes D, F, I, Q, U, V plus O. Suffix must be A-D (not E onward).