Both the main train companies serving Brighton and Hove said that services should be running more smoothly this afternoon (Monday 15 April).
Southern and First Capital Connect, which operates the Thameslink service, were affected this morning after a train used for engineering works derailed overnight.
The derailment damaged the track at Norwood Junction in London.
Network Rail said that the train was “rerailed” and the track repaired but it meant a morning rush hour punctuated by delays, diversions and cancellations for commuters.
The rail track owner warned that disruption was expected to last until about 3pm this afternoon. But most services had returned to normal by lunchtime.