Engineering work is taking place between Haywards Heath and Brighton, closing some lines.
All Gatwick Express services will run to an amended timetable, with extended journey times.
Southern trains between London Victoria and Gatwick Airport / south coast destinations will also run to a slightly amended timetable due to changes to the times of Thameslink train services that are diverted between London Bridge and East Croydon.
All day on Sunday, no Thameslink trains will run between Haywards Heath and Brighton, and a reduced service will run between Three Bridges and Haywards Heath. Your tickets will be accepted on Southern trains at no extra cost between Three Bridges / Haywards Heath and Brighton.
These trains will divert via Hove, with extended journey times.
You can plan your journey using the National Rail Journey Planner.