The Themes have been set by Warwickshire's Libraries and you can find out more on their blog.
The Books I have read so far and themes I think they match:
Diane Setterfield - Once upon a River - set in past, magical element
John Lewis- Stempel - The Wood - true
Tom Cox - Help the witch - Recommended, magical
Elizabeth Goudge - The little white horse - Children's author; Chosen by a member of staff; Blue cover; Carnegie Prize Winner