Thousands of train passengers endured travel misery on a key London to Scotland route today with the severe disruption likely to last all day.
Caused by an overhead wire collapse on the East Coast in Cambridgeshire, the problem led to some passengers spending Tuesday night on a train at London's King's Cross station.
East Coast services were severely disrupted, with no trains able to run between Peterborough and London during the morning.
Services run by First Capital Connect, Grand Central and First Hull Trains were also affected
As Network Rail (NR) and East Coast explained what had happened, Bob Crow, leader of the RMT transport union, said he had been warning about a shortage of overhead line crew and capacity for "years".
With the last East Coast train from King's Cross cancelled last night, the station remained open all night as passengers trying to get home refused to leave the train.
They included football fans trying to get home from Arsenal's Champions League match with Bayern Munich.
The London Evening Standard said a decision had been made to let the passengers stay on the train.
The trouble today followed severe disruption last week caused by an overhead line problem at Radlett in Hertfordshire.
At the same time as passengers were being delayed, the Office of Rail Regulation was issuing a damning report on NR's recent performance, accusing the company of "areas of poor management of the railways" and instances of "basic operational planning mistakes".
"Upon investigation damage has been caused to around one kilometre of overhead wires. Our engineers have worked through the night to carry out repairs and continue to work on the affected section of railway, but the scale of the problem means no trains will be able to run through this section until midday at least, when a diesel-only service will be able to operate."
The spokesman went on: "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.
"Train operators are providing buses where necessary and have lifted ticketing restrictions to enable passengers to travel via alternative routes.
"The cause of a dewirement on the Midland Main Line at Radlett last Wednesday was an infrastructure failure. All maintenance on this piece of infrastructure was up to date and maintenance staff numbers were not a factor."
The East Coast train company said: "East Coast services are being disrupted this morning following damage to the overhead power lines at St Neots last night.
"Network Rail have teams working to repair damage. They expect that a limited service of diesel trains may resume from 12 noon today."
The statement went on: "East Coast services are currently starting from, and terminating at, Peterborough. Our advice to passengers travelling to or from stations south of Peterborough, including London King's Cross, is to defer journeys until tomorrow, when tickets dated for travel today will be accepted.
"In addition, East Coast tickets are being accepted via alternative routes to London, including on East Midlands Trains' services via Sheffield, and on Virgin West Coast services.
"All ticket restrictions on East Coast trains have been lifted for the remainder of today. We apologise to all passengers affected by this disruption."
Mr Crow said: "We have been raising serious concerns about the shortage of overhead line (OHL) crew and capacity on Britain's railways for a number of years now.
"We repeated those points only last week when the lines came down at Radlett and now just days later we have another massive OHL failure on our hands. We cannot carry on like this."
He went on: "The chaos on services hitting hundreds of thousands due to cancellations out of central London as a result of the lines down overnight reinforces RMT's demand for a full review of OHL maintenance and emergency staffing numbers and capacity to cope with this growing infrastructure issue and a massive backlog of essential works."