and if it's before 8pm - go to Penge and get the bus back, that station's never manned ever!
Seriously though - it's my bet the reason they want to keep the south bound exist closed when the station isnt manned - is probably because they will hardly ever have staff at these gates during the peak time, despite what they say today. Therefore what sense is there in opening it at all? It will mean a member of staff will have to walk across the bridge and lock/unlock the gate daily. This will add extra burden to their daily chores, especially as the regular ticket police are unlikely to be there to do it for them. Cynical moi?.