Writing about spies, or intelligence operations in general, is a risky business, because the reliability of the information is almost always in doubt. There are circles within circles in the intelligence community, and sorting out truth from falsehood frequently is beyond the ability of even the most skillful, discerning outside investigator. When, on top of that, authors resort to surmise and conjecture to flesh out an uncertain story, let the reader beware.
In this case, the story is the life of Sir Claude Dansey, a chief of British intelligence organizations during World War II and an intelligence operative beginning during the Boer War at the turn of the century. Since, the authors concede, he was for most of his career "concerned with secrecy and deception, it is impossible now to trace all his movements." Add to that the British tradition of long-term secrecy in such matters, encouraged even further by the unhappy record of Soviet infiltration of British intelligence organizations, and it becomes readily apparent how monumental the task of writing a sound book on Dansey is, even 40 years after his death. No picture of him is even included in the volume.
Perhaps, Anthony Read and David Fisher, the authors of an earlier book on World War II spy operations that has been subjected to considerable criticism, should have waited in this case for more solid material. Then they might have been able to avoid such phrases as it is safe to assume and Dansey must have felt this way or that. These are a substitute for saying that the facts in the matters at hand cannot be established with certainty.