Commuters heading to the capital from Swindon this morning are being advised to expect disruption to their journeys.
There are currently long delays on the M4, while some railway stations have been flooded.
A spokesman for GWR said trains to and from London Paddington were experiencing disruption.
"Flooding at Didcot Parkway has resulted in the Station being inaccessible to customers travelling towards Oxford and Reading/London Paddington," he said.
"The platform towards Swindon, Bristol and South Wales is open. Customers travelling from Didcot towards London are to travel to Swindon and then back toward Reading/London Paddington.
"Newbury Station is now open. However the service through this Station will be delayed as on platform remains closed due to the flooding.
"A signalling problem in the Taplow Area (between Reading and London Paddington) is also causing delays to services."
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