Answer:
In general, but especially British people, tended to see Americans as less educated, and more opportunistic, people, who thrived better on earned money, and who were easy to sway by a quick buck, or better yet, by the chance to make money and spend it.
It was also believed that Americans were always attracted to the lifestyle of Europe, particularly England, and its culture. Americans were not seen as cultured, or noble at all, but they were perceived by the British as people who, aside from being good at using opportunities to make money, also sought social opportunities to be placed at the same level as British nobility and gentry.
In the short story by Mark Twain, "The Million Pound Bank Note", which was published in 1893, the author uses an American character, Henry Adams, who ends up washed away after a boating accident, in London, of all places. He finds himself in the situation of having found an envelope with a large amount of money, but in a single bank note. He tries to use it at first to survive, but soon finds out that he cannot and instead decides to begin reaping the rewards of not just having an assumed large sum of money, but also starting to gain a reputation through it. Aside from that, he builds himself from a no one, to a really reputable and important character who is soon raised to the level of celebrity.
In the end, what we see, is a sharp exposition of the way that Americans are seen and perceived as by Europeans, especially the British, and a contrast between the ideas that Europeans have on Americans, and the reality of who Americans are, in the figure of Henry Adams. I believe this is why Twain selected an American character living in England. To compare and contrast the diverging perceptions of the English about Americans, and the truth of how Americans are.