This comes from a book from last year,Triplex by Nigel West and Oleg Tsarev. Tsarev was a KGB officer given access to the archives as part of a soviet programme to publish details of the KGBs successes,
The KGB document is a report in April 1943 by Elena Modrzhinskaya, who was a top KGB expert on the uk.
The report in about my Gt uncle Biffy Dunderdale but it says that his father was the former manager of the vickers works at Kronstadt and his Mother Countess Demidov?
You know I didn't find again any Countess Demidova married to a Dunderdale. There is a daughter of Evgeniy Demidov (not a Count! from untitiled branch)who as married to an Englishman but the genealogies don't say exactly the name of that man. They married in the 1880s years.