UK Postcode (Full Format) Regex for PHP

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching uk postcode (full format), ported and verified for PHP. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your PHP project — whether you're validating in a Laravel validator, a WordPress plugin, or a standalone PHP script.

Php Implementation

<?php
// UK Postcode (Full Format)
// ReDoS-safe | RegexVault — Localization > Postal Codes

define('UK_POSTCODE_FULL_FORMAT_PATTERN', '/^(?:GIR\s*0AA$|[A-PR-UWYZ](?:[A-HK-Y][0-9][0-9A-HJKMNPR-VWY]?|[0-9][0-9A-HJKMNPR-VWY]?)\s[0-9][ABD-HJLNP-UW-Z]{2})$/');

function validate_uk_postcode_full_format(string $input): bool {
    return (bool) preg_match(UK_POSTCODE_FULL_FORMAT_PATTERN, $input);
}

// Example
var_dump(validate_uk_postcode_full_format("SW1A 1AA")); // bool(true)

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Postal Codes category and carries a ReDoS-safe certification. That matters for PHP developers because especially relevant in PHP where PCRE backtracking limits can trigger silent failures on malicious input. 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

Structure: area (1-2 letters) + district (1-2 alphanumeric) + space + sector (1 digit) + unit (2 letters). The inward code letters exclude C, I, K, M, O, V. GIR 0AA is the only postcode without a space.