Erm, arrest them without beating the shit out of them? What is presribed by law is 'reasonable force', clearly the video shows force which is not reasonable in the circumstance.
Where did I say that the Police should have let them go?
Because in order to arrest them, you have to stop them running away. If the only way to stop them running away is to disable them with the truncheon, then so be it. It's what the country has been begging for.