...we had a series of encounters with a group of kids who were attempting to "mark" the teen room of the library as their territory: pretty much intimidating anyone who came in to read, pretty much taking over the internet terminals in there, pretty much tearing up the place and cursing people out.
We don't have security cameras.
So I pretty much had to log people off the computers and tell them to leave, over and over. The most egregious offender, a 14-year-old with a rotten attitude and a mouth to match, I sent away for 2 weeks. He kept coming back. Eventually, I called the cops.
The cops were delighted to have the incident reports we had filled out and the photographs we took. They were pleased that none of us confronted the kids alone, but always with another witness. They were especially pleased that none of us had actually touched any of them.
The one boy who kept returning after his 2-week suspension tried to convince the police that I had committed assault because I blocked his path to the rest of the department by standing within 6 inches of him. If I had laid a finger on him, I have no doubt he would have charged me; if I had touched him, the police would have had to cite me.
It turned out differently than the events in England because we had appropriate actions to take and we took them. The one kid was removed, and the rest, knowing the adults would act in concert, didn't return for weeks. A few come in from time to time, as individuals, and they behave themselves.
The kids in England broke the rules. They should have been arrested by police who had documentation of their offenses gathered by the citizens who objected to their behavior. I understand the woman's anger, but anger is no substitute for proof.
Adults hold authority by virtue of our age and station. When we break the rules in pursuit of kids breaking the rules, except in cases where someone is in imminent peril, we forfeit that authority by acting like the lawbreakers.