I'm reading The Spectre of War: International Communism and the Origins of World War II (Princeton Studies in International History and Politics, 184) by Jonathan Haslam

And it basically says what communists have said all this time: Great Britain used Nazi Germany has a buffer to the Soviet Union and found them preferable to work with than the Soviets themselves.

They were hoping to press them into war with the Soviet Union and they did at that.