There was even a special list of victims drawn up, known as the “Black Book”. This contained the names of thousands of important writers, thinkers and politicians who were to be arrested or killed. The list included the likes of Virginia Woolf, HG Wells, Bertrand Russell, Paul Robeson, and Sigmund Freud (the Nazis didn’t seem to realise Freud was already dead at the time). Being in the list was later considered a badge of honour among British intellectuals, with the writer Rebecca West sending a pithy telegram to Noel Coward saying “My dear, the people we should have been seen dead with.”

As well as dispatching SS thugs to murder anyone they saw fit, the Nazis also had plans for ordinary male civilians. One document chillingly stipulated that “the able-bodied male population between the ages of 17 and 45 will, unless the local situation calls for an exceptional ruling, be interned and dispatched to the Continent”.

In other words, almost half the men in Britain would have been forced into slave labour in Europe, put to work in gruelling work camps, factories and mines. The effect on British society and infrastructure would have been devastating, and Hitler’s puppet state may well have collapsed as a result. Something the dictator might not have thought about while toasting his own triumph in the stately rooms of Blenheim Palace.