I don't want to make this too political, but I am really curious about people's perspectives. Please stay like close to the center in your response to my quest

I don't want to make this too political, but I am really curious about people's perspectives. Please stay like close to the center in your response to my question, obviously it is easy to make a kneejerk response. (I address this at the end of this comment.) So, we heard about a recent terrorist that he was banned from his Mosque (for being too radical), reported by other Muslims, and that the FBI also reported him to the UK. What do you guys think that the UK should do in this case? I mean let's take an absurd example of a petition by 50 people from mosques and community saying, "Hey, this person is not a member of our community but is spouting radical nonsense and wants to commit terror." In this case what should be done? I am drawing a complete blank, because it doesn't take long to prepare terrorist acts but until you do them you aren't really a terrorist. The only thing I can think of is something that even I can see would be a joke. If the government came to me and said, "hey we received over 12 people asking us to watch you because you are a terrorist. We'd like you to voluntarily participate in civilization training to better understand why terrorism is wrong. You'll get £200 for participating." But I can hardly type that without it sounding like a joke. I mean there's politeness but this sounds just absurd. (I added the £200 part because I think there is no way they would agree otherwise. But if it's not voluntary then that doesn't sit right with me either.) So in this actual, real-world case, what should the UK have done? I don't think increasing surveillance so that you catch someone between the 45 minutes it takes them to inform themselves how to perform terrorism, and going and doing it. People are pretty strong and powerful and have a million tools of every kind, more surveillance couldn't possibly help here, I mean the reaction time would have to be like seconds from when someone chooses to start googling how to do terrorism to making a concrete enough plot to be criminal. It's just not a solution. So returning to my question -- for the case I mentioned, what should we done? Note: I understand that it is easy to make a flippant, knee-jerk response. For example, it is easy to say, "if someone reports a muslim for radical speech the reported muslim should be thrown in prison without a trial, and throw away the key". I really don't want to start a thread like that so please don't respond if you have attitudes like this: I've represented your response in this last paragraph and ask you please not to derail this thread on this subject. Yes, it is very easy to deal with if totalitarianism is okay. I specifically say this because I know people in real life who would make exactly this response or one exactly like it. That is not my question and I've represented this position in this paragraph, no need to repeat it, and you would just get downvoted. In this comment I am asking for people's practical ideas that are close to the center, if they have any. Thank you.