$re = '/^([A-PR-UWYZ0-9][A-HK-Y0-9]?[AEHMNPRTVXY0-9]?[ABEHMNPRVWXY0-9]? {0,2}[0-9][A-HK-Y0-9]{1,2}|GIR 0AA)$";/m';
$str = 'G 83';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php