I'm not sure that anyone will ever be able to say with any certainity if this was ever actually spoken... unless someone turns up some very old recording equipment at 10 Downing street.  That said, I have to admit, this sounds like vintage Churchill wit.  What this is supposed to have meant (provided that it was actually said) was that Churchill had a deep, and at the time, growing contempt for Josef Stalin (also Joseph) and the Soviet Union.  From the time of the Yalta and Potsdam Conferences, Churchill had developed a dislike for Stalin and vice versa.  What is not debatable about the statement is that Churchill pushed for the U.K. and U.S. to continue the war after the fall of Germany by pushing the Soviets back out of Eastern Europe.  Churchill felt as if the Soviets were the biggest threat to Western democracy for the next term of history... turns out that he was something of a prophet in this regard.