What version of iTunes are you running?
If your Books have been transferred into your library they should appear in the Books source. You may need to enable this using the ellipsis tool ...
Physically these files should end up inside ..\iTunes Media\Books.
This screenshot is from a test library with no books in it, but shows which options should be enabled and where the books would be listed.
Hi Mr Computers,
thanks for getting back to me.
I've looked where you have helpfully suggested. The Books option is not in there!
However I've somehow managed to find a link to it online so I'm good for now.
I use a lot of Apple products but the restrictive nature of their software is beyond exasperating.