OK. Thanks for that. Can't use the paperclip attachment thingie, but I can right click on each photo, choose Photos, and it does go to Photos. However, it does not show up in my 'Last Import' album. That still shows my imports from yesterday from my camera.
I have imported two photos which I mailed to myself. In the 'Photos' view (top line in the Photos sidebar) they are inserted by the datetime the photograph was taken (not the date they were imported), which means they can be very hard to find if you don't know that datetime. However in the 'All Photos' album they do appear as the last photos, which is the way it used to work and which I prefer.
And the 'Use as System Photo Library' is still greyed out in Preferences.