A Bedfordshire power station is believed to be at the centre of a major power cut across chunks of the UK on Friday.
Little Barford Power Station, which is on the Beds-Cambs border, is believed to have disconnected from the National Grid for 4.58pm.
Two minutes later the Hornsea Offshore wind farm also failed.
The power cut affected nearly one million people and caused a blackout at Ipswich Hospital.
Blackouts were reported across the Midlands, the south east, south west, north west and north east of England, and Wales.
National Grid power was restored by 5.40pm but there was a knock-on effect for some train services, which continued to be disrupted into Saturday.
Andrea Leadsom, Secretary of State for Business, Energy and Industrial Strategy, said Friday’s power outage said there would be an investigation following the “enormous disruption”.
Duncan Burt, National Grid’s director of operations, said he did not believe that a cyber-attack or unpredictable wind power generation was to blame.
He told Radio 4: “We think that worked well; we think the safety protection systems across the industry, on generators and on the network, worked well to secure and keep the grid safe, to make sure that we preserved power to the vast proportion of the country.”
Rebecca Long Bailey, shadow business and energy secretary, said the impact of the power cut was “unacceptable” at a time when National Grid reported £1.8bn in profits and increased dividends to shareholders.