Reading about the riots in London, (which have yet to reach where we lived a few years ago in Putney), I see that lots of politicians were on holiday in August

Guardian: Boris Johnson heckled in Clapham Junction over London riots : “The London mayor, Boris Johnson, forced to return from holiday, reportedly in North America, visited Clapham Junction, the scene of some of the worst London rioting, on Tuesday.”

The Sun: PM David Cameron condemns riots after jetting back to deal with riots: “DAVID Cameron today condemned the “sickening” scenes of violence across England after jetting back from holiday to hold an emergency meeting on ending the three-day riots.”

Telegraph: London riots: Theresa May flies back from holiday

Guardian: George Osborne cuts short holiday to deal with stock market crisis

Politicians are not entitled to holidays. I mean, we can’t imagine the President of the United States on holiday out of the country, or even walking the Appalachian Trail. At worst The President is walking the beach or at Camp David, and that isn’t really a holiday, it is tele-work.
It seems the police were too on leave. They increased coverage from 10,000 to 16,000 officers on the third day? How about the second day? If they were available, shouldn’t they have been deployed?
This is best understood in a game theory context. We can build a simple model:
There are three types of players: Never Riots, Contingent Riots, Always Riots. The number of police > number of Always Riots. Number of Contextually Riots > number of police.
Normally the police outnumber Always Riots, so the everyday thugs are in prison.
However, the Contingent Rioter will riot if they think they won’t be caught. And they won’t be caught if every Contingent Rioter riots simultaneously, as then the rioters outnumber the police. Once a signaling mechanism is in place (the police are tied down over there, let’s riot here), the cost of rioting goes down, and those for whom rioting increases personal utility begin to riot.
The rioters must get some value from the rioting, otherwise they would stop. This value may be mercenary (I steal things which I can later use, and stealing is easier than working for it), social (I hang out with my friends), political (I am sticking it to the Man, I am changing policy, I am changing the world), or psychic (I like to watch stuff burn). In this case, there are a combination of things going on, but I suspect politics are the least of it.
Thanks to modern mobile communications (Blackberry, Twitter, etc.) the cost of signaling has decreased. The first signal was the police shooting of Mark Duggan. Now the rioters are as well informed as the police once were with their exclusive police radio.
Perhaps the rioters will get bored. Perhaps the police will get their act together and arrest sufficient number of Contingent Rioters to change the context.
I am also surprise no curfew has (yet) been imposed. This would give the police the authority to arrest anyone on the street. (And the number of arrests also seems quite low).
Wikipedia has a List of Riots. Of course this being wikipedia, there are many more recent riots than ones in the past. However as the cost of rioting decreases, we might get more of this in the future.