Although MI5 and SIS would not know it for another ten years (except, of course, that the moles Kim Philby and Anthony Blunt did), Krivitsky was providing details on two of the Soviet Union’s greatest operatives, the recruiters and early handlers of the Cambridge Five spy ring. It is unclear how many times Krivitsky met with the officers. But by the end of Krivitsky’s month-long stay in London, MI5 and SIS had obtained a wealth of information on the structure and operations of Soviet intelligence. At the heart of these revelations was the identification of Soviet operatives. Of those Krivitsky named, perhaps Arnold Deutsch and Teodor Maly attracted MI5’s attention the most, as these men ran the high-ranking CID source – the identification of whom was one of the primary goals in having brought Krivitsky to London. Krivitsky insisted that Deutsch, and then Maly, ran a high-ranking source in the CID – now widely accepted as having been one of the Cambridge Five. The question remains, however, as to whether the information Krivitsky provided in 1940 was sufficiently conclusive to have pointed could have prevented one of the worst disasters in British intelligence history.

Krivitsky informed British officials that an Austrian illegal named ‘Alfred’ Deutsch, holder of a doctorate in chemistry, arrived in the United Kingdom sometime in 1933–1934. The ‘bumptious’ Deutsch, as Maly described him to Krivitsky, initially arrived with his chief, the illegal resident ‘Reiff’ (Ignati Reif), but soon brought over his wife and child from Vienna. Strangely enough, Deutsch, who worked under the codename ‘Stefan’, also brought his mother-in-law not long after. His wife, a trained radio operator, worked on the OGPU staff. Deutsch apparently travelled on his own credentials, making it possible for MI5 to check police files on his entry into the UK. With details from the background check, Archer was able to confirm with Krivitsky that ‘Alfred’ was in fact Arnold Deutsch. Testifying to the efficiency of MI5’s Registry, Archer also ran a check on the name ‘Stefan’ and found the record of a telephone conversation between a previously unidentified Stefan and Arnold Schuster, the Second Secretary of the Soviet Embassy (and legal resident).