Rail travel between London Paddington and Heathrow was disrupted this morning after a train derailment.
Heathrow Connect services were suspended, with Heathrow Express operating a reduced service every 30 minutes.
Heathrow Connect tickets were being accepted on the fast link to the airport.
Network Rail said an empty train had passed a red signal outside the station, activating an automatic derailment on Thursday. Overhead power lines also came down.
The train had derailed in a siding, resulting in damage to infrastructure.
No passengers were on board at the time and there were no injuries.
A Great Western Railways spokesman said: “At the moment, we expect to be able to run around half our normal service in to and out of Paddington on Friday morning.
“We hope this will improve as further progress is made and we would ask customers to check before travelling.
“Passengers should expect GWR and alternative trains to be much busier than usual, particularly with additional people travelling to Ascot.”