Columbia subject headings:
Espionage, Soviet--Great Britain--History--20th century.
Great Britain. Special Operations Executive--History.
Secret service--Soviet Union--History--20th century.
Harvard subject headings:
Espionage, Soviet--Great Britain--History--20th century.
Great Britain. MI6--History.
Princeton subject headings:
Espionage, Soviet--Great Britain--History--20th century.
Great Britain. Special Operations Executive--History.
Secret service--Soviet Union--History--20th century.