Do you actually recruit anyone? I mean, the Civil Service does have people who have, in the past, engaged in political activism. Other professional organisations have also done so. It is actually accepted by most people in the UK that there is a right to protest. Criminal damage is a crime, okay, then that is not "protest" is it? You are putting those two things together for your own reasons, and coming together with this concept of "professional activist", which as you said earlier, is not actually a thing.
Peaceful protest is a right in this country, protected by the ECHR and even further back to the common law of England. Where do you get you information from "lets face there's no such thing". Its a been a thing for thousands of years.
So reasonably, I believe most people on this thread can separate protest from crime - they are not synonymous to most, and most employers can take their own view.