First Great Western (FGW) are only able to run trains on two of the four tracks into and out of Paddington.
This is because signal and safety equipment in the Maidenhead area has been affected by flooding.
Services are still running but at a significantly reduced frequency, and customers should expect delays to services.
Network Rail will be inspecting the signalling later this evening.
If they are unable to fix the problem, FGW say there is a high risk it will only be able to run an extremely limited service tomorrow morning (Tuesday).
FGW strongly advise customers to check before travelling, or consider alternative routes.
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