Train passengers are facing disruption this morning as “nationwide fault” is affecting rail services across the network, National Rail has warned.

“Trains across the network are having to start their journeys later because of this fault and some may also be subject to cancellations or alterations,” it said.

Problems are expected to continue until at least midday.

The issue is related to the communication system used between train drivers and signallers. The failure with the GSM-R system “is currently being investigated”, National Rail Enquiries said.

GSM-R is designed to enable driver 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.

According to National Rail, affected services include:

A spokesperson for Network Rail told The Independent: “We have discovered a fault with the railway’s radio communication system that is preventing it from automatically ‘logging on’.

“The back-up manual log-in system is being used instead causing a few minutes of delay at the start of the day. Once up and running the system is working normally and the impact for passengers is minimal.”

Dozens of trains have been affected. Particular problems are affecting London Waterloo, one of the three busiest stations in the UK. Trains to and from Salisbury and Yeovil have been cancelled as a result of communications problems. Many other trains are running 10 to 20 minutes late.

South Western Railway said in a message to passengers: “We have been informed of a national issue with communication systems affecting service this morning. This means that trains may be delayed before they start their journey.

“This is because it is preventing our train drivers from contacting the respective signalling centre this morning and a reset is having to be performed before the train can start its journey.”

At Heathrow airport, one member of staff talked of disruption at London Paddington on the express service, with cancellations blamed on “a problem with the on-board safety systems”.

Thameslink says that people should “travel using your normal route, however delays and alterations are possible”.

Scotrail said earlier that “services are subject to delays” but a spokesperson has since told BBC News that “things are operating normally”.

Travellers are being advised to check whether their services are running, allow extra time for their journeys and monitor live departure boards.

Frustrated passengers have been sharing their unhappiness across social media, with many complaining about their delays and others branding the service a “joke”, with little communication from train operators.