All lines are now open at St Neots after overnight repairs. There's disruption on First Capital Connect trains between Peterborough and King's Cross - buses will continue to supplement services between Peterborough and Biggleswade until 7am. Delays are also possible on East Coast trains.
Shortly before 2pm a spokesman for Network Rail said: "Following damage to more than one kilometre of overhead line equipment at St Neots last night our engineers have been working around the clock to restore the best possible service for passengers.
"Two of the four lines have opened to diesel traffic, allowing a limited service to run. From around 2pm we will be able to 'coast' East Coast electric trains under the damaged area which will allow more services to run where rolling stock is available."
"East Coast services are stopping additionally at Huntingdon and Peterborough to allow First Capital Connect passengers to make connections.
"Engineers will be going back in tonight to continue repair work. Further information about services on Thursday will be issued as soon as it is confirmed.
Rail passengers between London and Peterborough endured more morning misery when an overhead line problem led to major disruption to key services.
On the East Coast line, no trains were able to run during the Wednesday morning rush-hour.
There were reports that scores of passengers had been left stranded at London's King's Cross station overnight after the last train to Leeds was cancelled.
The latest overhead line problem is at St Neots in Cambridgeshire and is affecting a number of train companies.
On First Capital Connect, buses replaced trains between Biggleswade and Peterborough, with journey times extended by up to 60 minutes
Grand Central and First Hull Trains' services were unable to run between Peterborough and King's Cross, but it was hoped that a limited East Coast service would be able to operate between Peterborough and King's Cross after 9.30am.
A Network Rail spokesman said: "We apologise to passengers for the significant disruption this is causing to services. We're doing everything we can to repair the damage and get people moving as quickly as we possibly can."