Speaking to the BBC Radio 4 Today programme on Saturday morning, Duncan Burt, operations director at National Grid, said the power cut was an "incredibly rare event".
Andrew Adonis, a former chairman of Britain's National Infrastructure Commission, said National Grid had "some big questions to answer" about how a relatively brief power cut had caused nationwide mayhem on the railways.
LONDON (AP) - A power cut disrupted rail travel and snarled rush-hour traffic across large chunks of Britain, including London, on Friday, leaving passengers stuck on trains or unable to get home for the weekend.
A spokeswoman for Northern Powergrid, which serves Yorkshire and the North East, said 110,000 of its customers lost power, while at least 26,000 people were without power in the North West of England, Electricity North West said.
Back-up systems on Britain's electricity network "worked well" in response to the major power cut that brought widespread disruption to the country, National Grid has said.
Two minutes later the Hornsea Offshore wind farm also disconnected.
Ofgem has asked for an urgent detailed report from National Grid so we can understand what went wrong and decide what further steps need to be taken. Travellers experienced heavy delays and some train stations closed.
"This could include enforcement action". "The issue is now resolved and the system has returned to normal. And what was happening was the frequency was falling, the system could see this, and unfortunately, the way the system protects itself is by losing some demand", said Julian Leslie, the head of National Control at National Grid ESO in a video statement posted to Twitter.
The electrical grid operator in northeast England reported multiple power failures across the region, which affected the airport and metro system of the region's biggest city, Newcastle.
UK Power Networks tweeted on Friday evening: "We're aware of a power cut affecting large parts of London and South East".
The company has blamed the blackouts, that left more than 900,000 customers without power for several hours and transport systems reeling, on the loss of two generators in quick succession. Western Power Distribution said 90 percent of their affected customers had their power restored by 5:45 p.m., and work was continuing to restore power for everyone.