Good grief, which London do you live in? I've lived here for nine years, mostly in Brixton and Bermondsey.
> Drug dealing and use
Barely visible compared to virtually every other city I've been to
> prostitues loitering
Haven't been a thing in London for a decade, from what people tell me. Certainly never seen it. Evidently that business has moved wholly online.
> homeless people begging
A fraction of what it is in any comparable American city -- but certainly on the rise in recent years due to Tory policies.
> women being catcalled and harassed
This is definitely an actual problem.
> groups of youths congregating
Good grief, how is this even a problem? They're citizens and that's their right. A city which helps young people to congregate is doing its job. More power to them, provided they behave well.
> littering
Yes, that's sometimes a problem. Not so much associated with youth, in my experience: yobs come in all ages.
> Many of these 'pseudo-public spaces' (think Granary
> Square, More London, Canary Wharf) are enormously popular
> with families and businesspeople precisely because they
> have security personnel who do a good job of tackling
> these things.
There's nothing that prevents public servants from doing the same -- except of course that they're underpaid and diminishing in number, thanks to austerity policies. The bargain which is making here is:
1. Reduce taxes / enforcement of taxes on large corporations
2. De-fund and generally decrease the quality of public service
3. Shift the burden of responsibility for providing said services onto said large corporations, who now provide a facsimile of the commons, minus inconvenient concepts like civil rights (right to assemble, speech, etc).
4. Use people's growing discontent with public services to argue for lower taxes. Go back to 1 and repeat.
This is then propped up by a "Broken Britain" narrative like your own, which is, forgive the bluntness, tabloid-fueled bullshit. Despite the the government's diligent efforts to undermine public services, London remains one of the cleanest and cities on the planet, and is certainly doing better than at any point in its history.