Most of the antagonising actually came from people outside of Team GB. A couple of members from Team Scotland were the worst for it if you look back a few pages.
If you're really concerned about the members in Team Scotland or Team Ireland, Caz, then you should ask the that the players who applied take their Steam profiles off private and add a whitelist to the servers with a 'one player one ID' setup. Other than that you can't really be sure of whom these people are unless you start digging really deep by monitoring a nation's TS etc. but I imagine that you won't have the time which is fair enough.
I'm a bit disappointed though. If a team looks suspicious in the first place then why is it only being questioned now?