Investigations are underway into the cause of a major power cut that left nearly one million people in England and Wales without electricity.
The outage on Friday night left thousands of travellers stranded as it caused major disruption to the country’s railways as well as traffic lights.
Newcastle Airport and Ipswich Airport were also affected.
The power cut was caused after two power stations disconnected from the grid “near simultaneously”, the National Grid said, but ruled out any kind of malicious intent or cyber attack.
Duncan Burt, operations director at National Grid, told the BBC the power cut was an “incredibly rare event” but said back-up systems had "worked well".
He said when both power stations disconnected, the loss of power was so significant that a set of secondary back-up systems kicked in, but led to a proportion of electrical demand across the country being disconnected for a short period to help keep the rest of the system safe.
Mr Burt said National Grid was "very confident" there was "no malicious intent or cyber attack involved" in the incident.
Professor Tim Green, co-director of the Energy Futures Laboratory, Imperial College London, said earlier that he believed the two disconnected generators were at Little Barford and Hornsea Offshore wind farm.
Mr Burt said National Grid is due to provide a "a detailed technical report" to Ofgem, which has already urgently demanded information as to what went wrong.
He added: "This will require careful study to make sure that we do learn any lessons that come out of it and that the next time this happens disruption is minimised and hopefully a lot less than it was last night.”
In central London, trains began to run out of King's Cross late on Friday night after the station was shut down amid "apocalyptic" rush-hour scenes across England.
Passengers were filmed forcing their ways through the barriers in an attempt to get themselves on to the first northbound service after services were halted for several hours.
Manuel Cortes, general secretary of the Transport Salaried Staffs Association, called on the Government to be held to account for the “fiasco”.
He said: "Having our rail network brought to a standstill in this way is totally unacceptable.
"We've seen thousands of passengers stranded, unable to board trains and a number of cancellations; others have been taken off trains and onto the tracks. We need to know why this occurred and the lessons to be learned."