Tramps - Sempill became Lord Sempill and Baron of Craigever upon his father's death in 1934 (in fact while his espionage activities on the part of the Japanese were ongoing), and after he was found out he retired to whatever it is that retired peers who are persona non grata in official circles do (in his case, ISTR it was a fair amount of private flying). On his death, the Peerage and the Baronetcy were split, in a confusing tale which involves gender reassignation, hermaphroditism and court battles... In fact, probably a far more interesting (if prurient) and decidedly less well-known bit of history for a BBC documentary.
I know that Frederick Rutland was interned after Pearl Harbor and released when it became clear he wasn't a threat any more (around 1944/45). As I recall, he committed suicide a few years after the war ended.