Coming next in London: vigilantes. If the Metropolitan Police is perceived to be unable or unwilling to help (and it is so perceived), then small businesses on a single street and small residential areas will arrange their own self-defence - or pay freelance vigilantes to protect them.
This thought may be over-influenced by my previous Post, but there is already evidence for it in one or two areas of London - a street of Turkish shops protected by Turkish guys with baseball bats, for example.
The youths who have created mayhem in London for the past few days may be street wise, but they are not that street-wise. There are many uncovered faces on video and CCTV showing just who attacked the shop window or carried the TV away. Even if the Met never catches up with them, older (but not necessarily wiser) members of their own community will. There will be some beatings meted out and maybe worse.
All big cites have a potentially volatile underclass of young men (and sometimes young women), concentrated in poor districts, and all big cities have police forces which are selective in the services they provide.
At the Met, they are well set-up to protect Fortnum and Mason from peaceful protesters; less well set-up to protect small shopkeepers in Tottenham or Brixton from arson. And there are so many lunches and parties to attend.
So my guess is that fit young men, a few years older than the looters and just a little bit wiser, will see in the current mayhem some money-making opportunities. They will be making local businesses offers they cannot refuse - and probably will not want to refuse.