It sounds like that AH is indulging in a bit of handwavium. For example he's got the Germans introducing supersonic fighters in 1949/50. I'm sorry to say that given German designers of the era did not really understand supersonics (few did) a fighter with a performance of Mach 1.2-1.5 is pure sci-fi. I wouldn't be surprised if he is one of these people who believes in the 'Napkinwaffe' fighters and bombers.
TBO was a pretty plausible AH, Shattered World, OTOH, is getting into sci-fi/fantasy territory. I'm going to give it a miss.


Btw in @ Lord
Halifax did attempt to contact the Germans with an armistice proposal, though they took too long to reply to it and WSC found out. Essentially the Empire has
planned for the fact that an armistice might be a possibility, the famous Daventry broadcast instructed the Dominions that they were to act as they saw best.
In effect they chose not to recognise the armistice as being legal, or recognise the Halifax government.