National Rail wrote on X: “There has been damage to the overhead electric wires between London Paddington and Heathrow Airport / Reading, which is causing disruption to journeys between these stations.
“As a result, trains may be cancelled, delayed by up to 50 minutes or revised. Major disruption is expected until the end of the day.”
Elizabeth Line, Great Western Railway and Heathrow Express trains are all affected.
Trains in and out of London Waterloo are now back up running following major disruption on Thursday evening after a person died on the tracks at Clapham Junction and a separate fire on a train added to delays across the city.
British Transport Police confirmed officers were called to Clapham Junction at around 3pm on Thursday following reports of a casualty on the tracks. The person was pronounced dead at the scene.
The London Ambulance Service said it was alerted at 2.59pm to reports of a person hit by a train.
A spokesperson said: “We sent an ambulance crew, a paramedic in a fast response car, an incident response officer and our Hazardous Area Response Team to the scene. We also dispatched London’s Air Ambulance.
“Sadly, a person died at the scene.”
The incident led to cancellations and major delays through Clapham Junction, one of London’s busiest railway stations.
The Waterloo and City line was also suspended due to faulty fire equipment at Waterloo.
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A fire on a train at Wandsworth Town caused further disruption on routes between London Waterloo and both Barnes and Wimbledon.
National Rail warned that trains running through the area could be delayed or cancelled as a result of both incidents.
South Western Railway said passengers whose journeys had been heavily disrupted by the Clapham Junction incident could arrange their own taxis and claim reimbursement.
In a post on X, the operator said: “Because your journey has been heavily disrupted, you can book your own taxi and claim the cost back through the South Western Railway website.
“This applies to travel between any stations served by South Western Railway between London Waterloo, Portsmouth stations and Southampton Central.
”Passengers making a claim must provide their contact details, journey details, a description of events, and copies of their train tickets and taxi receipts.”