Stalin was playing Britain and France like a fiddle.
I don’t think Britain or France did them self any favors by sending minor ministers to Russia by slow boat to negotiate either. It really showed Stalin that they were not serious about eastern Europe which would mean that if war broke out the Soviets would pretty much be left standing alone. Stalin was far too shrewd for that so instead used the desperation of the Germans for a treaty to his advantage to absorb the Baltic states and buy time before he would have to face the Germans in combat.
Stalin was a one-man band; he was playing Hitler, too. Notice from the article about the banquet for the Anglo-French mission that Molotov didn’t attend; he sent a lackey instead. Even though Voroshilov and Shaposhnikov attended, they were strictly military men. Diplomatically, the Anglo-French mission was the second-rate game in town. Molotov was busy working with the Germans.
You can see from the articles that nobody in the West had an inkling of what the Germans and Soviets were up to, but the signs were there that the Germans and Soviets might cut a deal.
Nobody wanted a peace conference except Il Duce, and he didn’t really count. The Poles refused to talk with the Soviets and categorically refused to allow Soviet troops on Polish soil. That pretty much made moot the issue of an alliance with the USSR. And the USSR had some legitimate points about whether the western allies were really serious about fighting the Germans themselves.
It should have been apparent that the idea of an Anglo-French-Soviet alliance was a dead letter. The USSR was ripe for an approach by Hitler.