Based on training-videos I’ve seen...a particular socket wrench is all that is required, and a step-ladder. You could teach a 14-year old kid how to do it in 30 seconds. With everyone already dressed in hoodies around London...I don’t see where this can be resolved.
If the city wanted to really get tough....they might mount these on 60 ft tall towers.
Then a single small drone equipped with spray paint could disable dozens a day.