Kuhn does not get the subtle point that sending a low level envoy like Strang will make an alliance less likely than it already is.
Indeed. The Chamberlain government's lack of urgency in this matter is so striking it begs for more explanation. I suspect something along the following lines:
As of June 1939, the Brits believed their duty was to support the threatened government of Poland. And since Poles rightly feared Russians as much as Germans, Brits were in no hurry to jump into bed with Stalin. They rightly understood that Stalin, at best, would expect tangible rewards (i.e., Eastern Europe) in exchange for going to war against Hitler. At worst, Stalin's disdain for Brits & French could send their envoys packing, as it happened.
What the Brits could not possibly understand in June 1939, was that Poland had already become a lost cause -- no way could Poland survive a major war. It was only a question of who would be their new master -- Hitler or Stalin?
And as of June 1939 it was not yet clear which might be the worst new master -- many believed Hitler could save Europe from the evils of Communism.
As it turned out, the poor Poles suffered the worst of all possible outcomes -- first Hitler, then Stalin.