The work will be carried out throughout the weekend and will affect trains on Saturday and Sunday (April 5 and April 6).
We have outlined and simplified the details so you can plan your journey.
Saturday (April 5):
Engineering work is taking place between Lewes and Seaford, closing all lines.
Buses will replace trains, calling at all stations, between Lewes and Seaford all day on Saturday.
Sunday (April 6):
Engineering work is taking place between Raynes Park and Epsom or Dorking, closing all lines.
Replacement buses will run between Sutton and Dorking.
Engineering work is also taking place in the East Croydon area, closing some lines on Sunday morning.
Before 7am on Sunday morning, trains between London and Brighton will run to an amended timetable, by a diverted route.
Journey times will be extended by up to 10 minutes.
Before 8.45am, some stopping trains between East Croydon and London Bridge will be diverted and will run non-stop between East Croydon and Tulse Hill.
Replacement buses will run between East Croydon and Tulse Hill, calling at stations via Selhurst.
Saturday and Sunday (April 5 and April 6):
Engineering work is taking place at London Victoria, closing some platforms on Saturday and Sunday.
All day on Saturday and Sunday, a reduced service will run to an amended timetable to and from London Victoria.
Trains which usually run between London Victoria and Eastbourne or Hastings or Ore and trains which usually run between London Victoria and Littlehampton, will be diverted to run to and from London Bridge.
Trains towards London will be unable to call at Battersea Park.
Passengers travelling to Battersea Park from the Clapham Junction direction, you are advised to travel to London Victoria, then catch the next train to Battersea Park.
Trains that usually run between London Victoria and Reigate will be amended to run between Reigate and Redhill only.
Passengers should use alternative Southern or Thameslink trains to travel between Redhill and London.
On Saturday only, trains which usually run between London Bridge and Epsom will not run.
Trains which usually run between London Victoria and London Bridge will not run.
This means that no Southern trains will call at stations between London Bridge and Norwood Junction.
