Churchill and Stalin weren’t allies. They just had a common enemy.
Absolutely; Churchill knew that Stalin was Hitler with a red star instead of a swastika (and Stalin proved him right). Britain officially went to war to defend Poland; one of Poland’s invaders (from the west) was defeated. The USSR, which invaded Poland from the east at the same time, kept the whole thing for 60 years. Britain and France never realized the gains for which their countries had gone to war.