For the next idiot who mentions the alleged crime as being relevant to the cops' reaction, listen carefully:
You live in a country where the police are supposed to hand over those SUSPECTED of a crime, along with the evidence, to the justice system.
To spell it out more carefully, the police are not the judges of who is innocent and who is guilty, they don't get to decide what punishment to administer.
So whether they think they've just apprehended a modern-day Adolf Hitler or whether they suspect someone is guilty of jaywalking, or anywhere in between, dishing out punishment is not meant to be part of their job description.
That's aside from the fact that the chokehold used is illegal (at least according to reuters), I'm pretty sure it's illegal in the UK too. Ask yourself, should a police officer be doing something illegal?