I think there are a few similar questions that seem to suggest using app_data in the signed request (http://developers.facebook.com/docs/authentication/signed_request/) but I'm not sure if it will be possible to do what I am trying to achieve with it as I've never used it before.
If I have my Facebook 'Tab' Url as follows:
http://www.facebook.com/pages/PAGE_TITLE/PAGE_ID?sk=app_APP_ID
What I want to do is add an extra parameter on the end as follows:
&WT.mc_id=email-uk-8014
The reason for this is for tracking purposes and links will be sent out of the form
http://www.facebook.com/pages/PAGE_TITLE/PAGE_ID?sk=app_APP_ID&WT.mc_id=email-uk-8014
and the extra parameter will allow us to track the campaign id.
As you can see I have no way of knowing the value of the parameter beforehand as it depends on the link clicked by the user so is it possible to somehow get the value of the WT.mc_id parameter inside my iframe app?
app_data is the only parameter passed through other than the page ID and user's basic details (locale and if they do/don't like the page) - you'll need to use that for any sort of campaign tracking (or link elsewhere and redirect to the tab after capturing your analytics data)