known for years in advance that war was imminent and the British government had committed itself to join,
I have seen no evidence for that.
Do you have any?

Jim yesterday.
"They have agreed that there was no threat of invasion of Britain"
Jim today
"everybody is aware of that so it doesn't matter anyway"

From that Guardian review.
"Paxman's version of history is one that neither Gove nor Cameron could have any objection to being used as part of the national curriculum. "