He copied it from America. It pretty much started when a lawyer was filming police deal with a homeless man in a rough manner, so he started filming it and the police arrested him. He sued and won (Glik v. Cunniffe), and it set a precedent that it was a right to film in the police in public. People now go around filming things, including police stations to see if the police will respect their rights.I only just recently heard about this guy and there seems to be a lot of people copying him...
We don't have a First Amendment over here, but generally speaking, you are allowed to film the police in public:
"Members of the public and the media do not need a permit to film or photograph in public places and police have no power to stop them filming or photographing incidents or police personnel" - Met Police
If the police actually followed the above, seeing a person filming and just shrugged their shoulders and went about their day, then the person filming them would get zero views on Youtube and would eventually disappear into obscurity. Too many police officers don't seem to have read the memo though.