I've set the cookie as follows:
setcookie ("id", $get_info[0], 0, '/');
It's set in a file called login.php within the /admin folder. The path element only seems to be a limiter as opposed to a... widener(?).
I've set up a test page to find out if the cookie has worked properly, which just picks up the cookie and prints it. I've installed it with the same code in the /admin folder and the root folder, and it only works in the former.
The code for test.php is as follows. Is there perhaps another way of accessing it?
<?php
$id=$_COOKIE['id'];
print "$id";
?>