It is a tale which pits the serial escapers of Colditz against the traitor in their own ranks and the Gestapo against the double agents of MI9.

Britain's hopes are pinned on two of the war's unlikeliest heroes - a Jewish Glaswegian dentist and an East End black-marketeer in a story which ranges from Auschwitz to the Cabarets of Berlin.

Colditz is an iconic part of the British WW2 story, up there with Spitfires and D-Day and the subject of many books, films and TV programs. This strangely neglected facet of the WW2 story, but with a bigger story which for all sorts of reasons (not least of which were live security issues) has never been told and which Robert Verkaik has uncovered for the first time.