The work will be carried out throughout the weekend and will affect trains on Saturday and Sunday (April 12 and April 13).
We have outlined and simplified the details so you can plan your journey.
Saturday (April 12):
Engineering work is taking place in the Earlswood or Salfords area, closing all lines.
As a result, no trains will call at Earlswood or Salfords.
Engineering work is also taking place in the Southampton and Brockenhurst areas, closing various lines.
Trains will not call at Winchester and Southampton Airport Parkway.
Journey times will be extended by up to 45 minutes.
More engineering work is taking place between Wembley and Watford Junction, closing various lines.
From 8pm on Saturday until the end of service, no trains will run between Shepherds Bush and Watford Junction.
Sunday (April 13):
Engineering work is taking place until 9.15am between in the Littlehampton area, closing all lines.
Until 9.15am on Sunday, buses will replace trains between Littlehampton or Barnham and Chichester.
Journeys times will be increased when using replacement buses.
Engineering work is also taking place between Redhill and Reigate, closing all lines.
Replacement buses will run between Redhill and Reigate.
