Cantwell, J. The Second World War: A Guide to Sources London: PRO, 1998

This book is a really useful source to consider before you visit the Public Record Office on any project, whether personal or academic. If possible, use in conjunction with their online catalogue before you start any research. The book gives a very good idea of what is contained in the PRO, along with factual information about the Ministers of various departments, accompanied by several pages of information about the wartime roles of the various departments and ministries.