Curious if you've accounted for issues like metro area vs. city limits. It could very well be the case that the London contains more of it's metro area within city limits than San Francisco, thus increasing the divisor vs. the numerator.
SF has more unsheltered homeless people than the entire country of England according to these numbers. So even if SF's per-capita homeless rate is lower when you include some surrounding SF suburbs, it's still absolutely terrible and far worse than London.
And if you consider the whole Bay Area (which is closer to London in size), the homelessness rate remains very bad overall because homelessness is also very severe in Oakland and San Jose. Some of the smaller cities of course fair a lot better than others, but the total numbers of unsheltered homeless is very high across the whole Bay Area region.
Even Palo Alto has a high homelessness-per-capita rate when you count people living in vehicles as homeless. It's not nearly as bad as SF, but it's not good either.
