# Check UK postcode format
# Format is LD DLL, LLD DLL, LDD DLL, or LLDD DLL where L = letter, D = digit
$postcode = uc($postcode); # Could be removed if you use the /i regex switch
if ($postcode !~ /^(([A-Z]\d|[A-Z][A-Z]\d|[A-Z]\d\d|[A-Z][A-Z]\d\d)\s(\d|o)[A-Z][A-Z])$/i) {
    $error_msg .= "Invalid postcode for UK.<br /><br />\n";
}