Other have given excellent reviews on this episode so I will restrict myself to a few observations.
The plotters had a false care lined up in France so why did they bother with the charade in England. The PM could have been just as easily kidnapped in France. In fact, why just kidnap him, why not kill him ?
Japp was worried about his pension but for his hiring of Poirot he should have got a medal and a promotion.
The rescue of the PM did not do much good. German re-armament was not prevented