Hi!
The custom field value is submitted to the other page via the $_POST variable, as far as I can see from the form source, it should be in the $_POST[‘options’][‘aspf1_11’][‘postcode’] array key.
Please note, that the $_POST variable is cleared when the page is reloaded!
Usually, if I can’t find a posted value, I use var_dump($_POST); statement, it prints out everything, that is sent through the target page.