Brock, Peter. Against the Draft: Essays on Conscientious Objection from the Radical Transformation to the Second World War. University of Toronto Press, 2006. Partial preview available here via Google Books: http://books.google.com/books?id=5fe6gbDyDhEC&output=html
An earlier version of the chapter dealing with the formation of the Universities Ambulance Unit at Oxford is:
Brock, Peter. ‘Six Weeks at Hawkspur Green: A Pacifist Episode during the Battle of Britain.’ Peace and Change 28:2, pp271-293. Published online by Wiley InterScience, March 2003. Available by subscription (free to Oxford PCs).