From southern website:
We would like to apologise to passengers for the severe disruption caused by problems at London Bridge this morning.

While Network Rail successfully commissioned two new platforms as part of the Thameslink Programme, unfortunately shortly before 06 30 this morning the work resulted in major signalling and power problems halving the number of platforms available for use during much of the morning peak. As a result Southern services were diverted, terminated short or cancelled.

While Network Rail managed to restore two of the affected platforms, the remaining one is likely to be unavailable for the rest of today and passengers travelling through London Bridge will continue to experience delays.

Network Rail hopes to rectify the problem overnight and allow us to run a normal service tomorrow morning. Passengers are, however, advised to check Southern’s website before travelling.