The changes will affect journeys from Tuesday to Friday (June 30 to July 3).
Below is a full guide to help you plan your travel.
Maintenance will be carried out overnight at multiple locations, leading to late-evening and night-time timetable alterations on several routes.
Tuesday to Thursday (June 30 to July 2):
From 11.10pm each night until services finish, buses will operate between Maidstone East and Ashford International.
The 10.25pm and 11.25pm London Victoria to Ashford International services will be diverted between Otford and Ashford International, running via Sevenoaks rather than the usual route.
Passengers will need to change at Otford to connect with services towards Maidstone East, then continue their journey by replacement bus to Ashford International.
The 12.25am departure from London Victoria will run only between London Victoria and Maidstone East.
Services running between London Charing Cross/London Cannon Street and Maidstone East/Ashford International will terminate at Maidstone East and will additionally stop at Kemsing, East Malling, and Barming.
Wednesday and Thursday (July 1 and July 2):
Late-night services from London St Pancras International to Faversham (11.20pm and 11.50pm) will be replaced by buses between Ebbsfleet International, Gillingham (Kent), and Faversham.
These buses will serve all stations except Higham, Newington, and Teynham.
From 11.20pm until the end of service, buses will also replace trains between Sittingbourne and Sheerness-on-Sea.
Tuesday (June 30):
From 11.40pm until the end of service, buses will replace trains between Tunbridge Wells and Hastings.
These replacement services will run via Wadhurst, Battle, West St Leonards, and St Leonards Warrior Square.
Additional buses will also operate between Tunbridge Wells and Robertsbridge, calling at all stations along the route.
A small shuttle will run between Battle and Crowhurst.
Passengers requiring assistance at Crowhurst are advised to contact Southeastern’s accessible travel team before travelling.
Tuesday to Friday (June 30 to July 3):
From 12.30am until services end, buses will replace trains between Beckenham Junction (Tuesday, Wednesday and Friday) or Bromley South (Thursday) and Orpington, serving all intermediate stations.
Tuesday, Thursday, and Friday (June 30, July 2, and July 3):
From 12.10am until the end of service, buses will run between Gillingham (Kent) and Faversham, calling at all stations apart from Teynham.
A connecting bus will also run between Sittingbourne and Faversham via Teynham, with onward train connections from Faversham to Ramsgate.
Wednesday to Friday (July 1 to July 3):
From 12.30am until services finish, trains towards Orpington and Sevenoaks will not stop at Lewisham.
An accessible replacement bus will depart Lewisham at 1.10am, serving Orpington and all intermediate stations.
Thursday (July 2):
The 11.07pm London St Pancras International to Ramsgate service via Dover Priory will be diverted between Dover Priory and Ramsgate, taking an alternative route and additionally calling at Faversham and Margate.
A replacement bus will run between Dover Priory and Ramsgate, serving all stations except Thanet Parkway.
