Sorry Hugo, I didn't mean to post anonymously.
My forum is at
http://betyourlife.blogspot.com/p/forum.html. You'll find the members section down the bottom.
The 'Members Only' should be configured so that Everyone can view the structure as I want everyone to see the 'By Invitation Only' topic in the 'Members Only' forum, but only Administrators can create any more topics at that level.
At the moment there is only one sub-forum, 'Strategies', but all the sub-forum should be automatically available to Members without me having to add them in.
Thanks for your help.