By default, a navigation menu for a Book (hierarchical structure of pages) will appear in the left column only when you have opened one of the pages of the book.

How to get the Book navigation menu sticky in the left menu?

The Staffordshire CVYS site has all their static content organised in a book, and wanted this feature.

The trick was done by creating a new block (administer -> blocks), select 'PHP code' as input format. And copy the code that you find on Book Module: How to make a book navigation block appear on all pages.

Don't forget to change the value of $book_top_page on the 2nd line to the node number of the index of your book.

(Mind you, you can only do this when you are logged in as an administrator.)