A spy working for the Germans in the Second World War was found to be a subscriber to Naturist magazine, containing tasteful photographs of naked women and adverts offering “dynamic manhood” and “super strong arms”.

Whether Hans Larsen, a Norwegian, was an avid reader of the health and nudity journal is not recorded. But according to his MI5 file, released yesterday, it appears he may have used the pages of the magazine to conceal secret messages for his German controllers.

MI5 was tipped off that Larsen, from a whaling family, was providing intelligence about allied warships to the Germans. He was arrested and brought to England for interrogation at Camp 020, the special detention centre at Ham in Surrey

His MI5 interrogators discovered that he had been given instruction in the art of secret writing using a pellet of wax that had to be heated on to the end of a matchstick or toothpick.

His file revealed that, when he was arrested, one of the suspected outlets for his secret writing was a copy of Naturist dated March 1945.

He may have buried one message, using a coded system, in an article entitled “All-the-year-round natural fitness”. There was a pencilled circle around a line advocating that green vegetables should be steamed, not boiled.

Larsen was returned to Norway after MI5 had finished with him and he was sentenced to seven years’ hard labour.

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