British rail dismantled the South footbridge 17 years ago. So if you're waiting to catch your train on the wrong side of the barrier, you'll miss it -even if you run very fast :-(
Fill up the Oyster card at the machine on the platform. You'll need either cash or a Chip and Pin credit card. American cards with a mag stripe will **NOT** work. (ask me how I know...)
Four trains to Waterloo each hour: around 4 past, 20 past, 34 past and 51 past. Frequency down to 2 on Sundays. The level crossing can be down for up to 20mn at once some times, more usually 12mn.