Passengers have suffered major disruption on trains between Reading and London Paddington due to signalling problems.
The failure, between Slough and Southall, first occurred late this morning and has led to train cancellations and severe delays.
First Great Western are yet to provide an update about when normal service will resume, but have warned passengers trains may be delayed for about two hours or have their routes revised at short notice.
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The crash, which took place at about 7am today (Thursday), involved three vehicles. One man sadly died as a result of the collision and his next of kin have been informed.