Dozens of Hitler Youth members visited Britain on cycling tours shortly before the outbreak of the Second World War, newly declassified files show.
It was suspected they might be spies – especially after the now-defunct Daily Herald printed an apparent excerpt from a German newspaper containing suspicious sounding advice for the visitors.
But despite misgivings on the part of the security services, they were given a warm welcome across the country, particularly from Scout groups.
Printed under the headline "Nazis must be spyclists", the Herald article from May 1937 claimed the visitors had been given the following advice: "Impress on your memory the roads and paths, villages and towns, outstanding church towers, and other landmarks so that you will not forget them. Make a note of the names of places, rivers, seas and mountains. Perhaps you may be able to utilise these sometime for the benefit of the Fatherland.
"Should you come to a bridge which interests you, examine its construction and the materials used. Learn to measure and estimate the width of streams. Wade through fords so that you will be able to find them in the dark."
MI5 had doubts about the authenticity of the orders but were sufficiently concerned to collect dozens of police reports on the cyclists. The files released by the National Archives reveal that the Hitler Youth members visited factories, civic dignitaries and landmarks such as Windsor Castle.
However, they weren't welcomed everywhere they went. Detective Sergeant Leonard Ward of City of Sheffield Police wrote of one party who visited the city in July 1937: "It is known that Herr Hahn [leader of the German group] was found taking photographs of the surrounding country when he and the boys were on a visit to Edale recently, and this was resented by the residents."