I'll offer up this explanation from arch-conservative James Burnham (so please don't downvote the messenger) just for consideration on the idea that the "doing something about this", as SF tries so mightily, can make the problem worse. This is from 1964:
But what exactly is Skid Row? In reality it is not, other than incidentally, a spatial concept, but a functional one. . . Skid Row is the end of the line, and there must be an end of the line somewhere. ... The whole [reform] operation has proved to be, inevitably, an ideological illusion. Since Skid Row is not a static place, it cannot be abolished or rubbed out. The most noticeable consequence of this anti-Skid Row campaign has been merely to diffuse Skid Row, for a while, throughout the City.
I've elided a lot of supporting argument, the gist of which is that the denizens of Skid Row tend to form networks of support & attract institutions that maintain them. And while that level of maintenance looks (and is) rather squalid and miserable to outsiders, breaking it up is just replacing an organic support network with an artificial one which looks at the symptoms more than the roots.
I can't speak to London except that I guarantee London has a Skid Row, even if it's not physically located in London, if that makes sense.
Final disclaimer that I don't claim to have the answer, just pointing out one point of view that seems rather pertinent to 2017 SF despite being written 53 years prior, whatever moral valence you assign to the author & his politics.