UK National Insurance Number (NI) Regex for Go

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching uk national insurance number (ni), ported and verified for Go. Identity and credential patterns need both correctness and safety, since they're frequent targets for adversarial input. The snippet below is ready to drop into your Go project — whether you're validating in a Gin handler, a gRPC service, or a command-line tool.

Go Implementation

// UK National Insurance Number (NI)
// ReDoS-safe | RegexVault — Identity & PII > National Identity Numbers

package validation

import "regexp"

var ukNationalInsuranceNumberNiRe = regexp.MustCompile(`^(?!(?:BG|GB|KN|NK|NT|TN|ZZ))[A-CEGHJ-NPR-TW-Z][A-CEGHJ-NPR-TW-Z][0-9]{6}[A-D]$`)

func ValidateUkNationalInsuranceNumberNi(s string) bool {
    return ukNationalInsuranceNumberNiRe.MatchString(s)
}

// Example
// fmt.Println(ValidateUkNationalInsuranceNumberNi("AB123456A")) // true

Test Cases

When to use this pattern

This pattern is drawn from the Identity & PII > National Identity Numbers category and carries a ReDoS-safe certification. That matters for Go developers because Go's RE2 engine is inherently safe from catastrophic backtracking, but this pattern has been additionally verified for correctness. 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 include BG, GB, KN, NK, NT, TN, ZZ. Letters D, F, I, O, Q, U, V are excluded from the second character. Letters C, I, K, M, O, V are excluded from the first. Suffixes A-D indicate the benefit payment week within a quarterly cycle.