Hi,
I think I have solved this problem, which seems to relate to my confusion and some technical conflicts between bbPress and the recently retired Forums functionality in BuddyPress, not helped by the fact that although the BuddyPress Forum may have been retired it still lingers in bits of the interface, documentation and on the support forums.
It would seem the forums tab in settings>buddypress I was looking for is not supposed to be there anymore and the permission error message was misleading – The page does not exist – It is replaced by Settings>Forums
I had a page called forums which was not a forum and a some conflicted slug names once I sorted these I was able to set up a “category” with a number of working child forums. I also had to remove the menu item I had pointing to my forums page (which had been automatically created by the install) and replace it with a custom menu pointing to the root – the category page
So hopefully I can now try this on my live site. Thanks for all the help.
Ewan