If request on port 80, auto redirect to 443 equivalent - Moodle Course Management System

2.1 Installation of Moodle on a supported virtualmin server running Ubuntu Server 10.04 LTS

I have config file to say that the URI root should be https://mobilek16.net

When users put http://mobilek16.net, they get the error I have shown in screenshot.

I want to auto redirect them if the come in on port 80 but I can't get it to work.

I tried adding at top of index.php something like

<?php
if ($_SERVER['SERVER_PORT']<>443) {
header('Location: https://mobilek16.net');      
}
      ?>

But it is not working either.

Any assistance will be greatly appreciated ;-)