Hi Colin, I too am interested in Nicholas Pfeffer, and particularly in his mother Gulla Pfeffer. Gulla'sworked for a periodwith my father, Ernst Loewenheim, when he ran a photo agency in Berlin in the early 1930s, and we still have some of her photos. The National Archives list a file relating to Nicholas: HO 214/84 "PFEFFER, Nicholas Emil Carl: German national interned and sent to Canada; returned to UK to be near his mother, who had been detained and then released; repatriated to Germany". Following a request I made, some MI5 files on Gulla Pfeffer are available at the Archives (KV 2/2434 & KV 2/2435).
I would like to know more about your own interest. Perhaps we can correspond directly