mmm... difficult to say... good thread!
well, let me say this:

- if chamberlain resign because of the defeat in europe i can't see the reason to replace him with halifax: if britain wants to negotiate a peace treat chamberlaine is the right man, by contrast if britain wants to fight halifax is not suitable. so no place for halifax in any case.

- mosley??? come on, he was just a joke...

- negotiate a treaty: that's the key issue! in fact, it was simply impossibile. the nazi would never retreat in the west (france/holland/belgium) and, at the same time, britain could never accept nazi bombers/divisions in calais.

- in may '40 britain had very low morale but the country in many key fields was equal/superior to germany: trade, industry, technology, navy, intelligence..... and, yes, politics! churchill was not an alien, he was the product of britain's history.

- conclusion: someone else, maybe a fresh one(?), would replace chamberlain as PM and keep on fighting the nazi. i have no idea who, but someone would come out.

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If Hitler invaded hell I would make at least a favorable reference to the devil in the House of Commons
- Winston Churchill