Many thanks daveVk for offering to help.
I was certain that I had checked the output for those variables. However it turns out that I had not (and must have modified somethings) as straight away we have a problem (missing ID's);
var pop_parent_page = "";
var pop_child_page_id = "";
var pop_page_title = "Hanging Bags";
Looks like I'd removed;
Thats now resolved and I'm updating the CDN with the modified script (containing - alert) so that I can check the output there (handy test).