A track circuit failure is disrupting trains which travel to and from Brighton.
Train operator Southern said that disruption to and from Brighton was expected until 3pm.
Southern said: “fault with the signalling system at Brighton means all lines towards London are blocked.
“As a result, trains may be cancelled, delayed by up to 20 minutes or revised. This is expected until 3pm.”
The company added: “Lines between Brighton and Preston Park have reopened but there is a slight reduction in the number of platforms available at Brighton.
“This means that services that run between London and Brighton in both directions are now able to run again but some short-notice alterations remain possible.
“Other alterations and cancellations are also possible while Southern and Thameslink work to return services to normal, with some services having terminated and restarted at a different station to normal, for instance, at Haywards Heath or Three Bridges.
“Check before you travel this afternoon. If your planned train is affected then you may need to take an earlier or later train instead or change trains en route.
“We’d advise allowing an extra 20 minutes journey time as a result.
“This part of the network uses track circuits to detect the position of trains. These are electrical systems which monitor whether a train is on a section of track. They operate as part of the signalling system, which is designed to be ‘fail safe’.
“When a track circuit fails, the signalling system will interpret this as a train remaining in place, even though there may not be a train present at all or the previous service may have long since left the area.
“As a result, further trains cannot be automatically allowed on to the relevant section of track.
“Train drivers will be stopped by red signals on approach. They will then get verbal permission from the signaller so that they can proceed and will run at a heavily reduced speed as far as the next signal. This is so that the drivers will stop safely if they see anything ahead of them.
“In some areas, the sections between signals can be several miles long so this can result in delays building up.
“Even with shorter sections of track affected, there would still be a delay of at least a few minutes to each journey.
“Track circuit faults can be caused by a number of different issues, including electronic faults or obstructions on the track.
“Network Rail manage the signalling system, including track circuits, and their staff will be investigating as quickly as possible.”
Some passengers were diverted via Hove.
Others heading east faced replacement bus journeys from Polegate because of planned engineering works in the Eastbourne area.
Ah,, the weekly parody continues, dodgy points, a longer running series than the Archers, every week for decades on end.