There are severe delays on trains in and out of London Paddington this morning due to a signalling failure.
National Rail said a fault with the signalling system between Hayes & Harlington and London Paddington means that trains between these stations are disrupted.
Trains may be delayed by up to 15 minutes or cancelled, and Heathrow Connect services are suspended. The disruption is expected to continue until 12pm.
Services affected are Great Western Railway, Heathrow Connect and Heathrow Express.