No trains will run between the stations today (Saturday, January 15) and tomorrow (Sunday).
Network Rail said buses will replace Southern trains between Three Bridges and Brighton.
Trains between London Victoria and Brighton will run to a revised timetable and be diverted via Littlehampton.
On Saturday, only trains between London Victoria and Portsmouth / Southampton will stop at additional stations between Horsham and Barnham. There will also be a reduced service between Brighton and Lewes.
Buses will be replacing Thameslink trains between Three Bridges and Brighton.
A slightly reduced service will run between London Blackfriars and Three Bridges.
Thameslink services to / from Horsham will call additionally at Purley, Earlswood and Salfords.
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