Network Rail said that engineering work would affect services between Victoria and East Croydon on this weekend and over Christmas and the new year.
The track operator said: “This weekend Saturday 27 November and Sunday 28 November and over Christmas, from Saturday 25 December to Monday 3 January 2022, no trains will run between East Croydon and London Victoria. Most Southern trains will be diverted to London Bridge.
“On these dates Network Rail will continue work on the Victoria resignalling project, a major four-year programme of investment to upgrade signalling and track at key rail junctions on the south London lines into London Victoria.
“Over the 10-day Christmas closure Pouparts Junction, near Clapham, will be completely rebuilt with new track and ballast.
“Signal gantries to house the new signalling equipment, cables routes and power supply points will be installed along the lines from Balham to London Victoria.
“By doing some of the work in week-long chunks called ‘blockades’, Network Rail can give passengers the benefits of the upgrades much more quickly.”
Katie Frost, Sussex route director for Network Rail, said “Putting passengers first is at the heart of what we do, and that works across everything, including how we plan and deliver work.
“Blockades are a massive opportunity for us to deliver more efficiently, reduce overall disruption to services and ultimately do more work to improve journeys for our passengers.
“But we won’t forget that that the success of previous extended line closures was in no small part due to our strong focus on passenger and stakeholder management, and our close partnership with train operator colleagues.
“That’s why we’ll work closely with local stakeholders and train operators to ensure people who live by the railway, passengers and businesses are fully aware of the impact on their journeys and the alternative travel options available to them.”
Southern customer services director Chris Fowler said: “These engineering programmes are essential to give our customers the reliable, on-time services they rightly expect.
“We’re working closely with Network Rail and other transport partners to ensure our customers can get where they need to be when services are affected.
“Some journeys will take considerably longer than normal, so please check routes and times in advance.”
Network Rail added: “Later in the new year, from Saturday 19 February to Sunday 27 February 2022, Copyhold junction (near Haywards Heath) will be rebuilt with new track and points, and new track will be laid at Burgess Hill.
“The railway between Three Bridges, Brighton and Lewes will close for these nine days, with supporting weekend work before and after the main closure.
“In total, over 1,000 metres of track, 7,000 tonnes of ballast and eight sets of points will be replaced with new, more reliable equipment.
“On theses dates, buses will replace trains between Three Bridges, Brighton and Lewes.”