In the short story The Submarine Plans, Lord Alloway was the "Head of the newly formed Ministry of Defence" (Christie did not use the word "Minister"). Lord Alloway, formerly Sir Ralph Curtis, had been head of an engineering firm and had made his mark in the House of Commons. He was seen as an up and coming politician, tipped to be Prime Minister. At the end of the story, some time after the case, he did become the Prime Minister.
Poirot considered Alloway "a great man". He had "brains, resource, power." Poirot thought him to be just the strong man England needed as Prime Minister in the difficult days of reconstruction after the First World War. Captain Hastings, by contrast, took a dislike to him. He considered Alloway tactless, and all because he had, earlier, likened Hastings to the Dr Watson to Poirot's Sherlock Holmes!