Rail commuters on Thameslink train services are facing major disruption due to a damaged overhead wire, the operator has said.
Two out of four lines between London St Pancras and Bedford have been closed because of the issue.
Commuters have been warned there will be “significant reductions” in trains during the morning rush hour.
Network Rail engineers are dealing with the damage and Thameslink has advised customers to check before they travel.
Thameslink said tickets are being accepted on other routes including the London Underground.
However, Tube commuters on the Metropolitan and Jubilee lines have also been caught in major disruption.
A broken down train near Neasden has meant both lines are closed between Wembley Park and central London.
Jenny Saunders from Thameslink said: “Overnight there was significant damage to the overhead lines that provides power to our trains just south of Luton.”
There will be a “full investigation” and extra staff are on site to help.
“It’s not an acceptable service that we are delivering for our passengers this morning and it is imperative that Network Rail and Thameslink continue to work together over the coming weeks and months to understand what is happening when incidents like this cause disruption”, she said.
A spokesperson for Network Rail said: “We apologies for any inconvenience this disruption may cause.
“We are working hard to resolve the issues as fast and as safely as possible.”
The Labour MP for Bedford, Mohammad Yasin, said the service was “no better” than Northern Rail which is being renationalised.
“I met the rail minister a couple of weeks ago and mentioned all this and urged him to look into this case urgently because the people of Bedford are suffering,” he said.