The following came over the speakers when we waited for our train at Waterloo (roughly, can't remember the exact wording):
"Would the person at access gate x please stop what you're doing. You are taking a pee in a public place. You are on CCTV and a member of staff is on his way to your position."
"Would the person at access gate x please stop what you're doing. You are taking a pee in a public place. You are on CCTV and a member of staff is on his way to your position."