Sorry Ron, shows my ability to only absorb one piece of information at a time!
So, I went back to my snapshot, followed the procedure, started Xerte as guest, logged into management.php and changed to LDAP. So far so good - when I logged in as myself I still had the guest user projects.
However, as I was writing this I had a brain wave and tried another browser. I could then see my old projects so the issue appears to be browser caching among other things. So it all seems to be working for me now, I shall let the users have a try.
Many thanks for all your help, Ron.