As part of the Thameslink Programme there are major engineering works taking place from 20th December 2014 to 4th January 2015
There will be
NO Southern trains at all (these serve south west London including Gatwick)
There will be
NO Thameslink trains stopping at London Bridge - this is mainly the Bedford to Gatwick/Brighton routing - but these are being diverted from Blackfriars via Elephant and Castle
Southeastern (to south east London (e.g. Greenwich) and Kent trains will run but with some changes in the morning peak from Mon 22nd to Wed 24th December.
The closure this time will be to finish most of the works to the terminating platforms part of the station (Southern services) and facilitate the changes from mid-January to the 'through' platforms (to Charing Cross and Cannon Street) where from 12th January services to Charing Cross will not stop at London Bridge until August 2016
Details
here