The work will affect trains from October 26 through to October 27.
We have compiled all the details on these works so that you can plan your journey this weekend.
Saturday and Sunday (October 26 and October 27):
Major improvements works are taking place between South Bermondsey and Streatham and between Balham and Norwood Junction, closing some lines from Saturday to Friday.
As a result, no trains will run between:
London Victoria and West Croydon (via Crystal Palace).
London Victoria and London Bridge.
London Bridge and Streatham.
London Bridge and Beckenham Junction (on Saturday only).
Replacement buses will run between London Bridge and Streatham Common via Peckham Rye and Tulse Hill.
Journey times will be increased on replacement buses.
No replacement buses will run between Balham and West Croydon, Balham, and Beckenham Junction via Crystal Palace.
Paper tickets will be accepted on London Bus routes: 109, 157, 196, 201, 249, 255, 315, 322, 417, 432, 450 and 468 (between Balham and West Croydon).
Sunday (October 27):
Engineering work is taking place between Shepherds Bush and Watford Junction, closing some lines.
No trains will run between Clapham Junction and Watford Junction before 12pm.
Engineering work is also taking place from 12am until the end of the service between Three Bridges and Brighton and Lewes.
Replacement buses will run between Three Bridges and Lewes, Three Bridges and Preston Park, and Balcombe and Brighton.
Direct trains will run between London Victoria and Brighton, diverting via Horsham and Littlehampton.
These trains will be subject to extended journey times.
This will be the fastest journey option if you are travelling to / from Brighton.
Trains between Brighton and Ore will run to an amended timetable.