Thousands of commuters face severe disruption on their journeys home tonight, because of problems with overhead wires at Radlett in Hertfordshire.
Three train companies have been affected - Southeastern, East Midlands and First Capital Connect.
Trains are unable to run between St Pancras International and Luton on East Midlands services.
First Capital Connect is also suspended between West Hampstead and Bedford.
And Southeastern trains are suspended between Denmark Hill and Kentish Town.
More top news
Every Christmas gets a bit more desperate for one dog at Battersea. Can you help?
The problem has meant that no trains are able to run through Gatwick Airport rail station in West Sussex.
Schoolchildren found Eragon wearing a Christmas jumper in the bag filled with dog food, treats and a tear-jerking note, in a church.