The emergency repair to the water main on the South Circular from Monday didn’t hold back the flood. There are now bigger emergency works and the road is closed from Grove Vale to Wood Vale (Sydenham Hill is last exit if you are coming up from FH). Walking home from the Plough, it looks like the other regular leak at the bottom of Underhill might be kicking in as quite a bit of water coming down there.
Check TFL for bus diversions as each route is different but it seems little beyond the Plough until after Honor Oak Road.
Not sure how long it will be necessary. There’s an emergency water outlet at the Grove pumping water onto the street, lots of cones, two Thames Water vans and a couple of guys with big stopcock keys (the real name escapes me). They weren’t sure on the diversion timings.