Passengers have been urged to check their journeys on the railway in Sussex this weekend as planned engineering works could cause disruption.
There will be no direct trains between Brighton and London Victoria all day Saturday and Sunday while engineers work on the lines at London Victoria.
It means there will be no Gatwick Express or Southern services running to and from London Victoria.
A spokesman for GTR, the operator in charge of Southern and Gatwick Express services said: "If you were planning to travel with Gatwick Express, you should use other Southern or Thameslink trains between Gatwick Airport and London Bridge."
Trains to or from Ore, Eastbourne, Brighton, Littlehampton and East Grinstead will be diverted to run to and from London Bridge instead of to and from London Victoria. These trains will run to an amended timetable, with extended journey times.
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Trains to and from Horsham will be amended to run to and from London Bridge, and will run non-stop between Mitcham Eastfields and London Bridge.
As well as this work, there is major work planned on the East Coastway between Brighton and Lewes, so all lines will be closed.
Buses replace trains between Brighton and Lewes all weekend.
Trains will run to an amended timetable from Lewes to Eastbourne and Hastings. On Saturday, a reduced service will run between Lewes and Eastbourne.
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