using referral in php contact form to store previous (referring) page

Hi,

I have a website with multiple links 'book now' to a contact form. I want my php contact form to record which 'book now' link was clicked through to the booking form. So I know without the customer telling me, which part of the website they are coming from.

On the sales page:

Code:

---

<a href="<?php echo($domain); ?>/contact.php"><img src="book.gif" alt="Book Now" border="0" /></a>

---

Then we use POST on the contact form and here is an example of the code (in part):

Code:

---

<?php
if(isset($_POST['Submitted'])) {

        unset($message);
       
XXX

  if(!count($Errors)) {
    $SendTo = "XXX";
    $Subject = "".$_POST['name']. ": booking";
    $FromString = "From: ".$_POST['email']."\r\n";

    $Indhold .= "I found the website by: ".$_POST['source']."\n";
    $Indhold .= "Looking at this tour: ".$_POST['tourname']."\n";

    if(@!mail($SendTo,$Subject,$Indhold,$FromString)) {

---

I found the following thread which is very close to what I am trying to achieve.
webdeveloper...Display-URL-of-previous-page

Here is the thing, I have a few links to the contact form on each URL (the same page, different tour codes linking to same contact form). So I can't use

Code:

---

$ref = getenv("HTTP_REFERER");

---

as I will still not know exactly which tour they were looking at.

So I guess each link needs to have it's own variable, but I can't see how to store this on my contact page.

Any help appreciated.
Thanks,
Andy