gistfile1.txt

    protected function _validateUkPostcode($postcode) {
        // Permitted letters depend upon their position in the postcode.
        $alpha1 = "[abcdefghijklmnoprstuwyz]";                          // Character 1
        $alpha2 = "[abcdefghklmnopqrstuvwxy]";                          // Character 2
        $alpha3 = "[abcdefghjkpmnrstuvwxy]";                            // Character 3
        $alpha4 = "[abehmnprvwxy]";                                     // Character 4
        $alpha5 = "[abdefghjlnpqrstuwxyz]";                             // Character 5

        // Expression for postcodes: AN NAA, ANN NAA, AAN NAA, and AANN NAA with a space
        $pcexp[0] = '^('.$alpha1.'{1}'.$alpha2.'{0,1}[0-9]{1,2})([[:space:]]{0,})([0-9]{1}'.$alpha5.'{2})$';

        // Expression for postcodes: ANA NAA
        $pcexp[1] =  '^('.$alpha1.'{1}[0-9]{1}'.$alpha3.'{1})([[:space:]]{0,})([0-9]{1}'.$alpha5.'{2})$';

        // Expression for postcodes: AANA NAA
        $pcexp[2] =  '^('.$alpha1.'{1}'.$alpha2.'{1}[0-9]{1}'.$alpha4.')([[:space:]]{0,})([0-9]{1}'.$alpha5.'{2})$';

        // Exception for the special postcode GIR 0AA
        $pcexp[3] =  '^(gir)(0aa)$';

        // Standard BFPO numbers
        $pcexp[4] = '^(bfpo)([0-9]{1,4})$';

        // c/o BFPO numbers
        $pcexp[5] = '^(bfpo)(c\/o[0-9]{1,3})$';

        // Overseas Territories
        $pcexp[6] = '^([a-z]{4})(1zz)$/i';

        // Load up the string to check, converting into lowercase
        $postcode = strtolower($postcode);

        // Assume we are not going to find a valid postcode
        $valid = false;

        // Check the string against the six types of postcodes
        foreach ($pcexp as $regexp) {
            if (preg_match('#'.$regexp.'#', $postcode, $matches)) {
                // Load new postcode back into the form element
                $postcode = strtoupper ($matches[1] . ' ' . $matches [3]);

                // Take account of the special BFPO c/o format
                $postcode = preg_replace ('#C\/O#', '#c/o #', $postcode);

                // Remember that we have found that the code is valid and break from loop
                $valid = true;
                break;
            }
        }

        // Return with the reformatted valid postcode in uppercase if the postcode was
        // valid
        return $valid ? $postcode : false;
    }