Can you point to historical documents supporting your statement?
Everything I have read suggests Britain was determined to have Stalin as a military ally even if he demanded both Poland and Finland. That British foreign policy became more pronounced after Churchill became PM.
Surely you don't mean the same Churchill who very much supported the post WW1 expedition to Russia to aid the White Russians, and made the statement that bolshevism should be strangled in it's cradle.
You need to come up with some historical documents yourself that Churchill, one of the leading anticommunists of his time, was pro-Russian proir to Germany's invasion of Russia.