The lower levels wreathed in engine smoke, the villas of the rich gleaming white on the higher decks. (1.3)
The difference between the upper class and lower class is striking in this view of London-on-wheels. The rich live in fabled white buildings; the poor live in literal filth.
Tom could not get at him, because Melliphant's family had paid to make him a First Class Apprentice, while Tom, who had no family, was a mere Third. (1.23)
Looks like even in the future people are divided by class lines, and as Tom's background tells us, people have no control over which class they're born into.
"That's what comes of living in a slum on the lower tiers. [...] When the Big Tilt happened they both got squashed flat as a couple of raspberry pancakes: splat!" (1.37)
Melliphant shows us classism at its worst. Not only is the lower class in greater risk merely because of where it's forced to live, but people in higher classes, like Melliphant, don't even view the losses of lower-class lives as a tragedy. It's funny to people like Melliphant.
Tom loathed [the Gut]. It was always noisy, and it was staffed by workers from the lower tiers, who were dirty and frightening. (2.3)
Even though Tom is the victim of class discrimination, he isn't immune to classist thinking himself. While "dirty" isn't that subjective (when you're dirty, you're dirty), seeing the lower class as "frightening" might be due to class prejudice.
"Just because they live in the nether boroughs and don't pronounce their Hs doesn't mean they're fools." (2.31)
After all the class prejudice we've seen, this is shockingly progressive—especially coming from Valentine, who has no real regard for human life whatsoever. What did these people do to earn his respect? Also, does this show us that Valentine is more than a cartoonish villain? Is he more complicated than he seems?
Top Tier hangs over the city like an iron crown. [...] It is the smallest, highest, and most important of the seven Tiers, and, though only three buildings stand there, they are the three greatest buildings in London. (7.1)
Ever heard of the 1%? The Top Tier is like that. How is it that something so small in number gets to be so important and so powerful?
We are experimenting with ways of turning [poo] into a tasty and nutritious snack. We feed our prisoners on nothing else. Unfortunately they keep dying. But that is just a temporary setback, I'm sure. (16.22)
Yikes. Experiments done on prisoners without their knowledge? Totally sci-fi, right? Would never happen here... oh, wait. This did happen at the Holmesberg Prison in Philadelphia (source). So much for the City of Brotherly Love.
"We have no hospital down here. These are prisoners. [...] Criminals. They don't require medical care." (16.36)
These prisoners aren't even second-class citizens. They're no-class citizens, treated as livestock. Hey, by the way, how did these people get into prison in the first place? If you're living at the lowest level of society without any resources, and things get desperate, maybe you'd become a criminal, too, right? Don't tell that to the Top Tier in London, we guess.
Who cared if people were dying of heat stroke down in the Nether Boroughs? Good old London Good old Crome! (18.1)
Can a country (or giant rolling city, in this case) be considered great and wonderful if it has no regard for its lower-class people? The way a country treats its poor is a big indicator of its value as a whole. What do you think of London here?
All [Katherine] could think of were the thousands of Londoners who were toiling and dying in misery so that a few lucky, wealthy people like herself could live in comfort. (18.7)
This has pretty much been Katherine's father's philosophy: other people suffer so that my family doesn't have to. Now Katherine is taking it upon herself to repent for the sins of her father. Would you think of her differently if she didn't?