Our reporter Heather Cartwright is at Waterloo Station.

She says there are some delays at the station but the mood is calm as people try to figure out their next move.

The Gatwick Express says its services may be altered or terminated before reaching their destination due to the communication fault.

Passengers affected can use their “ticket at no extra cost on Southern and Thameslink services via any reasonable route.”

LBC’s travel reporter Joanne Webb says commuters should check their train service’s individual website before setting off this morning.

She said: “My best advice is if you need to get a train this morning, just go onto their website, see what’s happening with your individual train.

“It’s probably going to be delayed. You may be lucky, it may only be delayed by about five minutes, but some trains have actually been completely cancelled.”

Southeastern Rail says all of their routes are open for passengers to travel as a nationwide communications issue causes disruption to the service.

In a post on X, they told passengers that affected trains are delayed “between 5 and 20 minutes.”

Trains across the UK are having to start their journies later because “of the failure of the onboard GSM-R system,” says National Rail.

GSM-R is a system that allows drivers and signallers to communicate digitally at all times, including while trains are in areas such as tunnels and deep cuttings where previous analogue systems did not work.

 It was rolled out to increase safety and reduce costs by replacing the patchwork of inefficient legacy systems which were expensive to maintain.

ScotRail says its services are now “operating well” with “minor delays” in places.

Earlier, we reported that ScotRail was experiencing delays due to the communication issue affecting National Rail. 

ScotRail is assuring passengers that the signalling fault affecting service “does not affect the safety of train running” as alternative methods are in place.

National rail says affected services include:

• The Elizabeth Line
• South Western Railway
• Gatwick Express, Great Northern, Southern, Southeastern and Thameslink services
• Scotrail

National rail says the delays are due to a “nationwide fault” relating to the communication system between train drivers and signallers.

Services across the National Rail network may be subject to disruption, delays and cancellations or changes due to an issue with the system drivers and signallers use to contact each other.

Follow our live blog for updates.