In some ways, what happens in The Invisible Man is all these people's fault. If the old woman didn't think Griffin was experimenting on her cat (which he might have been – he's experimenting on a cat, at least), and if the landlord didn't try to kick Griffin out, then this book would have a happy ending. Actually, we're not sure about that: after all, by the time Griffin is making trouble in the house on Great Portland Street, he's already contributed to the suicide of his father.
So, as far as the story is concerned, these two people are here in order to push Griffin over the edge, causing him to become invisible before he's fully tested out the formula or figured out a way to reverse it. These characters also show us that people in London may be as curious and gossipy as the people in Iping.
All Griffin wants to do is steal some wigs and stuff – is that so much to ask? But the costume shop owner keeps locking doors and waving his gun around. In some ways, this guy is foreshadowing Kemp, who also makes Griffin's life difficult by locking doors (or ordering doors to be locked) and waving a gun around.
The real reason we're interested in this unnamed guy is that he looks a little strange: he's "a short, slight, hunched, beetle-browed man, with long arms and very short bandy legs" (23.9). In other words, this guy may not look like everyone else. Who does that remind us of? In some ways, he's kind of like Griffin, the albino. Does Griffin say to himself "hey, maybe this guy and I can get along"? No. Instead, he bashes him on the head (23.20). This is a reminder that Griffin isn't very good at making friends, even when there's potential for a connection.
How many people are there in the London section of this book? A lot, actually: the people in the Salvation Army march that nearly traps the Invisible Man; the urchins who follow his footsteps (21); all of the workers in the department store; the police that are called to catch the IM (22). Oh, also, there are the cab-drivers and the woman who gets into the cab (21.7) and…well, London's a pretty busy place.
Thinking back on all the people we know in Iping, we notice that unlike the villagers, Londoners don't have names or jobs. We could ask two questions here:
(1) What does that comparison tell us about London compared to Iping? What is the difference between city and country living? Does Wells characterize one in a more positive light?
(2) Since the section in London is narrated by the Invisible Man, what does this say about him? Even in a big city, the Invisible Man doesn't get along with people and he doesn't even bother to learn their names. For all we know, Londoners might be really friendly (as friendly and neighborly as Iping villagers). But the Invisible Man is too much of a jerk to notice.