The problem is affecting services across much of the country, including Edinburgh, North Wales, Manchester, London and Southampton.
Services run by Virgin Trains, London Midland, CrossCountry and Arriva Trains Wales have all been hit by the issue.
Network Rail said the disruption for passengers across the network is expected to continue until 3pm.
Passengers travelling south with Virgin Trains are being diverted via Stafford, extending their journey times by up to an hour.
Some ticket restrictions have been relaxed in a bid to help travellers reach their destinations by other routes.