Thameslink has said the disruption has now ended.

The operator said in a post online: “If you've been delayed at your destination by 15 minutes or more, you should apply for Delay Repay compensation.”

Great Western Railway has said the communication systems has now been resolved and services are “no longer affected”.

National Rail Enquiries said some services may still be delayed “by up to 90 minutes or cancelled whilst service recover”.

“Major disruption is expected until the end of the day,” an update added.

A Network Rail spokesperson said: “Due to issues with radio communications, train services in the South West and south have been subject to some delays this morning.

“Staff have worked to resolve the fault, and train services are now returning to normal.

“We apologise to passengers for the disruption caused to their journeys.”

Our travel correspondent Simon Calder writes:

The busiest station in the UK for “normal” trains (excluding the Elizabeth line) is London Waterloo.

It is the hub for state-run South Western Railways.

Data from RealTimeTrains.co.uk shows delays of over an hour beginning at around 9am, with trains from Reading, Portsmouth and Honiton in Devon arriving over an hour behind schedule.

The train due in from Windsor at 9.23am finally arrived at platform 14 at 11.09am, nearly two hours late.

Many trains due to operate were cancelled due to rolling stock, drivers and guards out of position.

Even though the systemwide fault is now fixed, delays and cancellations are likely to continue into the afternoon and possibly affect the evening rush-hour.

The compensation bill for delay repay is likely to run into hundreds of thousands of pounds on South Western Railway alone.

If you have been affected by this morning’s rail disruption, we want to hear from you.

Get in touch by emailing maryam.zakir-hussain@independent.co.uk

National Rail has said disruption towards Haywards Heath is expected until 1pm.

The operator said passengers can travel on the following lines at no additional cost:

• Thameslink services between London and Brighton
• Southern services between London and Haywards Heath

The radio fault that took train lines down this morning also occurred in December 2024.

The nationwide fault was linked to faulty GSM-R radio systems, which allow communication between train drivers and signal operators.

Widespread delays also took place in 2024 as a consequence of the radio fault.

Speaking to Sky News during the 2024 disruption, railway journalist Nigel Harris said the fault was "very, very rare" and something he had not experienced in 40 years of working in the industry.

Train journeys are often disrupted, as we can see from today’s travel chaos with South Western Railway. Passengers who are caught up with long delays and cancellations are entitled to a partial refund – or the full cost of the ticket for a really long delay.

But the rules are complex and change from one train operator to another. And Eurostar, which runs trains from London to Paris, Brussels and Amsterdam, has a quite different policy on delays.

Travel correspondent Simon Calder has the key questions and answers:

Gatwick Express has said the fault with the radio system “has now been resolved” but services can still expect delays or cancellations.

A statement on their website said: "The fault with the radio system between the driver and the signaller that is affecting services on the South England network has now been resolved. Some services may still be delayed by up to 90 minutes or cancelled whilst service recovers.

“Major disruption is expected until the end of the day.”