Trains from Portsmouth and Havant to London have been seriously delayed due to signalling problems near Guildford, caused by cable theft.
As a result the service is operating on a reduced timetable, with journey times being delayed by up to half an hour.
Trains leaving from Portsmouth Harbour to London Waterloo at 15 minutes past the hour have been cancelled, and those returning from London Waterloo to Portsmouth Harbour on the hour have also been cancelled.
South West Trains tickets will be accepted on First Great Western and Southern services on any reasonable route.
Passengers are reminded that limited services whish are running will be very busy.
A spokeswoman for South West Trains said: ‘A number of our services have been disrupted today as a result of cable theft resulting in a signalling problem between Havant and Guildford. We apologise to passengers for any inconvenience caused by these delays. Network Rail engineers are working to resolve the problem as quickly as possible.’
Last week South Coast commuters faced delays after a cable was stolen from the Littlehampton area.