I'm guessing they probably wouldn't want to go to war with the Soviets, not just because they were wrapping up WW2, but if I recall correctly I did read on here that the US and UK put a lot of effort into the media to make the Soviets look better, and that because if it a lot of Americans and British had good opinions of the USSR during the war (obviously this changed after, though).
It's worth noting that until the fall of 1945 there is no corresponding US "Unthinkable" plan. The US Joint Chiefs of Staff are on the record in this period as stating that Soviet intentions were "benign" and never even really discuss the possibility of war with the USSR. Even the first plans from late-'45 were more specific strike studies rather then comprehensive warplans. It wasn't until early-1946 that the closest American equivalent of Unthinkable, the first of the Pincher series, emerges. And even these plans all consistently rejected both preventive and pre-emptive war, dealing solely with a Soviet initiated war. Only General Patton at all advocated an offensive war against the Soviets, and the vast bulk of his subordinates, colleagues, and superiors thought he was militarily and politically crazy for it. And even Patton never actually really
studied attacking the Soviets like the British did, just made mouthed off on the idea.
In other words, if attacking the USSR in mid-1945 was unthinkable for the British military leadership, then it was uncontemplatable for the US one.
then 25/26 is WSC asking for a defensive study that starts image 29 (image 27/28 seem to be a misplaced summary from the earlier studies). Interestingly he asks for the study on the assumption that France and the Low Countries are powerless to resist and asks about the possible retention of bridgeheads in Europe and airbases in Denmark to cover naval operations in the Baltic (some obsessions never die).
The response from the adults is that they are reasonably sanguine about defending the British isles. In view of soviet superiority “there can be no question of holding a continuous continental front”, and that there is no merit in the idea of defending bridgeheads on the continent, reasons spelled out.
So the Brits at least seem to have moved from contemplating pushing the Soviets out of Poland to contemplating Dunkirk II followed by Battle of Britain II.
Well, there's a bit more to the defensive study that provides a bit of extra-context to what Churchill is thinking. Namely the bit that comes before the sentence with "the assumption that France and the Low Countries are powerless to resist". Specifically it says: "
If the Americans withdraw to their zone and move the bulk of their forces back to the United States and to the Pacific, the Russians have the power to advance to the North Sea and the Atlantic." (Emphasis added)
That adds a bit of additional timeframe which thinks of dealing with an Soviet attack somewhat later on, perhaps in 1946, when the demobilization of Anglo-American forces in Europe would have left them basically decrepit and incapable of offering meaningful resistance on the continent, rather then in the summer of 1945 when WAllied forces made Operation Unthinkable, if still unthinkable, then at least contemplatable. Despite the Soviets own demobilization up through the end of '47, the fact the Soviet demobilization was shallower and slower paced and then abruptly was followed by a military build-up from early-'48 onwards meant the gap in strength between the respective sides conventional forces really only widened during the course of the 40s. The writing off of almost all of Continental Europe in the opening phase of the war makes sense in such a context and is a continuing theme with the later US and British Warplans of the late-1940s and some of the early-1950s.