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.
Has your journey been affected? Tell us in the box below.
Top Ten Articles
The Met Office has issued a yellow alert for Windsor and Maidenhead, Slough and Wokingham, warning that rain moving eastwards across the south of the country may turn to snow in some places.