Ben Macintyre attends the UK premiere of Operation Mincemeat earlier this year. The movie, starring Colin Firth, is an adaptation of Macintyre's book about a secret British military operation from the second World War. Photograph: Tim P. Whitby/Getty Images for Warner Bros Colditz is a very well known story. Why have you written a new book about it? It is a question I asked myself before taking on the project. There are 73 books on Colditz counting all the French, Polish and reprints. Many of them are much the same book. They all tend to follow the same pattern until...