In 1937–8, at the height of the Great Terror, Nikolai Yezhov, head of the NKVD, visited Joseph Stalin in the Kremlin no fewer than 278 times for private meetings lasting a total of 834 hours. So far as is known, no previous world leader had ever spent so much time closeted with his intelligence chief.

Working for Soviet intelligence during the Terror was a high-risk occupation. Many of those who led the paranoid hunt for ‘enemies of the people’ at home and abroad themselves fell victim to the paranoia. In 1939 Yezhov was found guilty of the phenomenal feat of spying simultaneously for the secret services of Britain, Germany and Poland. 

The purge of mostly imaginary traitors in Soviet foreign intelligence was so extensive that by 1939 the NKVD’s London station was manned by only a single officer, who was so poorly informed that he admitted to Moscow that he knew almost nothing even about Kim Philby, later recognised as its