Profile field edit delegated authority

I have CB working fine, however I have a requirement to add two custom profile fields such that one user group with moderator privileges can edit/view one field during profile edit but not the other, while another group can edit the second field and not the first.
IE effectively hierarchical delegated authority. 
I had understood that a field could be assigned to an “access” level so that normal ACL could limit access to the field, but I cannot see any such configuration option for individual CB fields anywhere. 
I do see the “Access” option for core user fields but not CB fields and I believe that I need to use CB fields to leverage CB list filters.
Is this possible and if so, how please?      
Very latest Joomla and CB installed…

There is not such functionality built in. CB Moderators have full moderator privileges. There's no way to limit them to 1 specific field. It's possible to limit editing of a field to moderators only using CB Conditional, but it'd be available to all CB Moderators and not specific ones.

The only way to really do that would be a custom form that would submit to a custom backend for saving that field. Then you'd be able to add whatever ACL you want to that process. This can be done either by using 3rd party form extensions as a few do integrate with CB or you could use CB Auto Actions + HTML to do this.

With CB 3.0 we'll be looking into new ways of assigning moderator permissions allowing per-user moderation (e.g. User A moderates User and full permission system for what that moderator can edit (e.g. manage profile, but nothing else).