Commuters on the Elizabeth Line and other trains into London face major disruption today after a points failure near Slough.
Great Western Railway passengers are being warned to expect cancellations, delays and revisions until 3pm.
The problems are affecting services across the GWR network, centring on London Paddington station.
Meanwhile, there are severe delays on the Elizabeth Line between Hayes & Harlington and Reading.
Tickets are being accepted on London Buses, Great Western Railway and South Western Railway, and there is good service on the rest of the line.
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Separately, there is no service on the Jubilee line between Finchley Road and Waterloo while engineers fix a signal failure at Green Park.
The issue has also resulted in severe delays on the rest of the line.
This morning’s disruption comes a day before much of the Tube network is set to grind to a halt due to strike action.
Drivers from the Rail, Maritime and Transport union (RMT) are due to walk out on Tuesday and Thursday in a dispute over ‘proposed compressed four-day working arrangements’.
The strikes, which will last from midnight to midnight on both days, will mean no service on the Circle line, the Piccadilly line, the Metropolitan line between Baker Street and Aldgate, and the Central line between White City and Liverpool Street.
Services are expected to go ahead on other London Underground lines on both days.
However, the Tube will start late and finish early, with commuters advised to finish their travels by 9pm on both days.
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