Yes, Churchill’s own work is still the best source on the war, although it contains some errors, intentional or unintentional. Of course, there are many things like codebreaking that he could not mention at the time.
I am still unclear on why Halifax declined the PM offer on May 9 when he could have had it. The movie has him saying: “My time has not yet come.” I think that that was unlikely. It is clear that Halifax and Churchill had a mortal fight over peace negotiations later that month. The movie has George VI coming to visit Churchill to promise his support.
IMHO: Lord Halifax it would seem did not want the burden of the office of PM at that time. In short, he was scared to assume that role.
I think Halifax knew hard decisions would need to be made and he didn’t want to do it but was willing to bide his time and step in later.
The hard decisions that Churchill makes is amazing and may not have been made by a lesser man. Sacrificing the men at Calais so that the rescue at Dunkirk could happen....Sobering.
Because Halifax knew that only a coalition with Labour could direct the country through the war and he knew that Churchill would be a better leader of such a coalition than he would.