By as early as 1939, Britain was well aware of the strength of actively-pro-Zionist-sentiment in the USA (and indeed, the strength of more generally fascist sentiment therein).
That throughout the WW2 years, she tolerated an unseemly level of Zionist-instigated terror within Palestine (Lehi and Irgun terror) – was doubtless influenced by this understanding.
And so? For her to so deeply place her trust in any ‘US good intention to deliver on Historic Palestine’s 1922 League Mandate promise’ post WW2 . . . and to nonetheless, jointly facilitate the UNSCOP political process . . . evidences a serious laxity and inattention-to-duty!