In this talk, Professor Kevin Ruane (author of Churchill and the Bomb, a BBC History “Book of the Year”), explores the relationship between Winston Churchill and the Oxford scientist F. A. Lindemann, known almost universally as the “Prof”. For over thirty years, from the 1920s to the 1950s, the Prof was amongst the very closest of Churchill’s personal friends as well as his scientific advisor as Prime Minister during the Second World War and later in the early Cold War. In that key advisory role, and taking advantage of his intimate association with Churchill, Lindemann arguably exercised more influence over government than any scientist before or since – an influence that was both positive and, some areas, highly controversial and even dangerous.