National Rail says an earlier issue affecting communications between trains and signallers has now been fixed – but warned significant delays are likely to continue.
“Some services may still be delayed by up to 90 minutes or cancelled whilst service recovers,” it said.
South Western Rail has also warned commuters to expect significant delays and alterations.
“Whilst the issue has been fixed we are working towards returning the service to normal as soon as possible, however will mean significant delays and alterations will still be ongoing whilst this takes place,” the train company said.
Passengers are still being warned to expect significant delays across the network, with trains either held in stations, delayed, or cancelled. “Timetables and platform information may change at short notice,” SWR added.