If a general fired his scouts and spies saying they were not worth the money as the enemy never attacked and he could "hire them back when he needed them" you would see a flaw in that plan. Trump did exactly this, defunding Obama era advanced warning staff other measures put in place due to H1N1 and Ebola. Hell even Mitch had to reverse course saying actually they were given a playbook, they just never read it. The buck stops at the initial catastrophic failure. Chamberlain will never be forgiven, neither will Trump, history will be blunt.
Had the British a presidential term system and not the parliamentary system where Chamberlain resigned as PM in May 1940 under a threat of a vote of no confidence (the government comprising more than one party and the others would not longer serve under him), he could possibly have rewritten history in the time remaining in his term a fair bit. Who would remember every detail leading up to the conditional surrender of the UK to German forces?