The FBU is probably the strongest after the Trains but in all honesty, it isn't that strong. Supposedly, to join now, you need to pass a DBS check but I've seen this ignored. Where we used to have to be of a certain stature, this has all gone to accommodate, let's just say, smaller people. This is all very well but I have also seen these "smaller" people unable to lift 40kg very easily. What did the union/brigade do? They made it policy to not have any dummy casualty (in training) weigh more than 35 kg. How much do you weigh?
I wouldn't join the brigade now. It is a trap. I was almost sacked for refusing to wear a mask during the scamdemic. I was called into my borough commanders office, after he had received a complaint from a female firefighter, that o had called myself a fireman. At training school, if you can call it that now, they are given a snitch line to call. There have been incidents of suicide from new recruits over being asked to make tea! On the surface that goes down as bullying. I'm not saying that hasn't happened but what it does point to is why or how did someone like that get through. We have to deal with shit that isn't nice.
As for the lad you know, HIS face probably doesn't fit. Without knowing his past, I can't say but I bet he is fit enough, I bet he is strong enough and I bet he'd play the game and make the teas during his apprenticeship?