It is one of the many contentions in this lively, provocative and indeed contentious book that the order to stop the German tanks in May 1940 before they reached Dunkirk can at last be explained rationally: Hermann Göring, commander in chief of the Luftwaffe, was high on morphine. In this state, he blithely told Hitler to leave the final coup de main to his airmen. Only too late did Hitler wake up to the fact that Göring’s judgement of the situation was wrong. He ordered the tanks forward, though not in time to stop the British escaping across the Channel.

The Dunkirk episode is one of many historical puzzles that the German novelist Norman Ohler sets out to solve in this book, which exposes the seamy, drug-soaked underside of the Third Reich. It should be said at the outset that this is not a history of drugs in