Tor Idar Larsen has written a biography over Finn Thorsager (http://surfcity.kund.dalnet.se/norway_thorsagen.htm ). The book is on 209 pages and covers Thorsager's career from his youth via the Norwegian Air Force and the RAF to the end of his career in the SAS. It's a very nice book and includes some unique images. Books about the Scandinavian pilots in the RAF are very rare and this book covers this period very well. Unfortunately, the book is written in Norwegian and thus will only be accessible to a Scandinavian market. In addition, it lacks an index, which makes it difficult to use as reference in the future (many other Norwegian pilots features in the book). However, these are only minor issues and if you're a Scandinavian with interest in this period this is highly recommended book!
Available from: http://www.finnthorsager.com/index.html