A technical fault has caused delays to Great Western Railway (GWR) services.
GWR has confirmed that a fault with the signalling system at Gloucester has results in all lines being blocked.
This has caused all services between London Paddington and Cheltenham Spa via Swindon and Gloucester to potentially get cancelled, delayed or revised.
A spokesperson for GWR has issued the following advice for customers.
"During this disruption, if you wish to use local buses as an alternative means of transport and the local bus is not accepting GWR tickets please purchase a ticket on the bus, keep it and send it, together with your train ticket, to us to claim for a refund."
They added: "CrossCountry are conveying passengers between Gloucester and Cheltenham Spa in both directions until further notice.
"Arrangements have been made for Great Western Railway rail tickets to be accepted for these journeys."
Network Rail colleagues are on site investigating the fault and it is hoped it will be resolved soon.
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