Southern services face cancellations March 1st & 2nd. Plan travel between Havant, Portsmouth, Fareham, Southampton.
On Saturday and Sunday, Southern trains stop between Havant and a few places, including Portsmouth Harbour, Fareham, and Southampton Central. South Western Railway buses replace those trains and run between Havant and those locations. But trains still go from London Victoria to Bognor Regis, and from Brighton to that same place.
You can use Southern tickets on South Western Railway only between Fareham and Southampton Central.
Sunday means more changes, especially near East Croydon. They are fixing stuff, so some lines shut down all day. Trains will run less often between East Croydon and Purley, and the schedule changes.
Trains from London Victoria will only reach Redhill, instead of Reigate. Take other trains between Redhill and London using Southern or Thameslink. Trains to East Grinstead start at East Croydon and still end at East Grinstead.
Fast trains won’t run between London Bridge and Caterham or Tattenham Corner. Some trains change routes from London Bridge to East Croydon, going through Norwood Junction, not Peckham Rye. They skip Streatham, Streatham Common, Norbury, Thornton Heath, and Selhurst. These trains now also go to Caterham or Tattenham Corner.
There is also work between Polegate, Eastbourne, and Hastings, closing lines. Buses replace trains between Polegate, Eastbourne, Hastings, and Ore. Trains still run between Hastings and Ashford.