Travel disruption caused by "cracks" appearing on a number of Hitachi trains will continue on Sunday and into next week.
On Saturday Great Western Railway (GWR) was forced to cancel a "significant" number of long distance train services, including those between Swansea, Cardiff and London, after cracks appeared on a number of trains.
As a result a number of Class 800 series Hitachi trains from several train companies were taken out of service for checks as a precaution.
It has now been announced that disruption is expected to continue on Sunday, May 9 and into the following week.
Timetables are being published as "soon as possible", but GWR warned that rail replacement services are extremely limited. Local services are running but are expected to be busy.
A statement released on Saturday evening said: "The problem continues to be investigated by Hitachi and once trains have been checked and cleared, we hope to be able to release them back into service as soon as possible. A further update will be provided in due course. "
There will be no service, or only an extremely limited service, with no alternative means of transport available on the following routes:
Passengers on these services are advised not to travel.
Rail Minister Chris Heaton-Harris said routine checks of Hitachi trains early on Saturday morning identified cracks on part of the chassis of some trains.
He said: "Safety is always our absolute priority, so these trains have been taken off the network to undergo full and rigorous checks.
"Hitachi are working to complete these strict precautionary checks. Trains will be returned to service as quickly as possible once they are fully approved as safe by the manufacturer.
"Whilst some trains are starting to be reintroduced, disruption is likely for a prolonged period, particularly on GWR. I share the frustration of passengers who are experiencing significant disruption, and would ask people whose journeys are affected to check before travelling. I’ve asked operators to ensure extra staff are on hand to help people complete their journeys safely, to increase their communications with passengers, and to make information on refunds and compensation clear."
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General secretary of the National Union of Rail, Maritime and Transport Workers (RMT), Mick Lynch, said: “RMT is fully aware of the issues that have led to the cancellation of services on LNER today and that similar problems with cracks appearing in the fleet on Great Western are also emerging.
“Hitachi needs to ensure the highest safety standards and properly investigate and rectify the issues.
“This situation demonstrates once again that it is reckless for the rail companies and the DfT to move the industry to diluted, risk-based maintenance regimes which extends maintenance cycles on rolling stock or on the infrastructure, whether that be on the mainline railway or on the tube and metro services, to cut costs and strip out staff.
“The railway needs to be maintained rigorously and to the highest possible standards to protect the travelling public and the staff and that will remain RMT’s key demand.”