$re = '/([A-PR-UWYZ](?:[A-HK-Y][0-9](?:[0-9]|[ABEHMNPRV-Y])?|[0-9]([0-9]|[A-HJKPSTUW])?)) ?([0-9][ABD-HJLNP-UW-Z]{2})/i';
$str = 'DA11 0AA
WC1H 1AA
N1 2AA
';
preg_match_all($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