He added: “Even as famous, prominent leaders in public life, these men confess their pride in their Anstalt (institution), [and] appear whenever possible at the annual reunions.”

The admiration went both ways, with George Olive, Dauntsey’s School headmaster, writing in the Thirties: “I found the headmasters of [the NPEA] to be men of wide vision and great practical ability.”

The British, Dr Roche said, were impressed by the “preternatural physical development” of German pupils who managed to match the British on the football field.

However, admiration was not universal, Dr Roche has found, with the Nazis critical of public schools’ “aristocratic exclusivity”, which contrasted with the NPEA’s aim to educate “boys from any background, be they the sons of labourers, farmers, or the lowliest officials”.

Research has shown that the British schoolboys were disturbed by the secular devotion of their German counterparts for the Fatherland, which they praised in “song and recitation” and “salut[ing] the flag with ‘Heil Hitler’ […] very smart with heels clicking etc”.

British pupils were critical of the Germans taking their singing “so seriously and patriotically” without the “fun and rioting” they were used to.

Dr Roche has written that both sides hoped building friendly relations between their elite youngsters would help both nations in future.

There were eventually 40 NPEA schools across the Reich by 1945.