I received this from Network Rail this afternoon:
Earlier today a hole believed to be four metres deep was found in the Forest Hill area. This means that two lines into London Bridge are closed. As a result, Southern services into and out of London Bridge are severely disrupted with many services diverted, starting/terminating short of their destinations or cancelled. These alterations will remain in place until the end of service today.
More than 50 tonnes of ballast, which supports the track, is on its way to site to fill the hole and engineers will be working through the evening and throughout the night to try and fix the problem. Our aim is to have the railway fixed for tomorrow morning, but holes like this can be unpredictable. Until the ballast is packed into the hole we won’t know for certain if the hole is stable or not.
Passengers are advised to use either Victoria or Blackfriars tonight. Southern tickets are being accepted on London Buses, London Underground, South West Trains, Southeastern and London Overground services on any reasonable route.
Passengers are advised to check before they travel at Nationalrail.co.uk
Until 10pm:
Horsham passengers are advised to travel via Victoria or Blackfriars
Caterham and Tattenham Corner trains will start as normal from London Bridge but may be subject to delay or cancellation due to diversion on the way in
Victoria to London Bridge trains are still planned to run but are being diverted via Peckham Rye, some services may only run between London Victoria and Beckenham Junction
Uckfield trains will start as normal from London Bridge but may be subject to delay or cancellation due to diversion on the way in
Thameslink services between Brighton and London Bridge are starting/terminating at Gatwick Airport
Trains between London Bridge and Eastbourne will run from either London Victoria or East Croydon.
Southern tickets are being accepted by London Buses and London Underground on any reasonable routes.
After 10pm, until 4am:
Network Rail will close all four lines between Norwood Junction and London Bridge while they make repairs to the infrastructure.
As a result, there will be no services between London Bridge and East Croydon running via New Cross Gate. All services will run via a diversionary route and passengers should expect disruption and longer journey times. Customers wishing to travel to intermediate stations will need to use London Buses to complete their journey.