Passengers face a miserable afternoon as hundreds have been left stranded on trains due to a power cut.
The electrical fault at Radlett station has also meant the Luton to St Pancras line - which runs through Harpenden and St Albans - has been suspended until further notice.
Initial reports suggest a freight train pulled down the over head wiring at Radlett, but this is unconfirmed.
First Capital Connect workers are trying to free people who are trapped on the trains - but are unsure how long this will take.
People have taken to Twitter to vent their anger, with @DharshiniSky saying: "Shambolic handling of overhead line problems. Now very cold, late and cheesed off."
Tickets are being accepted on alternative routes.