Seriously not an issue. Lived here forever. I've seen bits of the very top and bits of the very bottom. It's a right-wing youtube myth that there are out of control zones in London. Sure there are sketchy areas and some are grotty AF with homeless camps in some surprising places but it's absolutely nothing like SA townships. Of course there's violence but it's proportional to the size of the city. The serious spice epidemics and the deprivation that go with that are mainly in other parts of the country, and sadly people shit in the street everywhere. I'm sure I could find these things if I went looking for them but none of this is 'part of life' for your average Londoner and very few people have experienced any of this except shitting tramps who are reasonably common in central. Although I did once see a guy shit his pants on the tube.