A signalling problem at Balcombe has meant rush-hour delays and disruption for thousands of commuters heading home to Brighton and Hove by train.
Replacement buses were running while engineers worked on the problem. Journeys were estimated to be delayed by about an hour and some services were cancelled.
Network Rail said: “Please check before you travel this evening as there is disruption to trains on the Brighton main line following a problem with a set of points near Balcombe.
“Our engineers were on site soon after the problem occurred. However, the points were jammed in the wrong position and we could not run trains until they were made safe.
“Passengers are encouraged to check before they travel as their journeys will take longer than normal.
“Buses are in operation between Brighton and Three Bridges to help with overcrowding.
“We are sorry for the disruption to your journey.”
Update: Southern said: “We are now able to operate trains north of Haywards Heath. However, services still remain disrupted.”
The problem came to light after lunch, with replacement buses running from about 3.30pm.
Southern added that the delays and disruption were expected to last until the end of today’s timetable.
It added that those seeking compensation should use the “delay repay” scheme. For more details, click here.
If your journey has been disrupted due to the signalling problems at #Balcombe please claim delay repay here http://t.co/8n3A0wieQf
— SouthernRailUK (@SouthernRailUK) April 24, 2015