BTP seem to think they can step in to "help" during any conversation with a customer where there might have been a disagreement or where you've had to repeat something.
You've just told someone to top-up, maybe you don't think they should travel till they've sobered up or they are absent mindedly tapping their card on a 'No Entry' gate.
We deal with customers like this everyday, sometimes they get a bit annoyed when you intervene but most of the time we've handled the situation and we can move on.
Step forward the BTP who when they like to hang around (not if we did need them) listened in to your chat and decide to repeat what you've said, more aggressively, invade the customer's space and ask such helpful questions as "are you stupid?" or " are you too drunk to understand what you've been told?"
What has this achieved other than to get customers back up further or make a situation you have sorted out worse. Perhaps they get to feel like a big man, and it's always the men who do it!
Most of us want to help customers not treat them like they're scum. We need less of the BTP hanging around and more customer service staff!