Image copyright PA Media Image caption Clapham Junction station in south London was one of the areas where lights went out

The government has launched an investigation into Friday's huge power cut which affected nearly one million people across England and Wales.

Business Secretary Andrea Leadsom said a committee will look at what happened.

Train passengers were stranded, traffic lights failed to work and thousands of homes were plunged into darkness during the blackout.

The investigation will consider whether the procedures followed by National Grid are fit for purpose.

Mrs Leadsom said the power outages "caused enormous disruption", adding: "National Grid must urgently review and report to Ofgem."

The Energy Emergencies Executive Committee, carrying out the inquiry, will also explore whether there were any technical problems, plus how well National Grid communicated about the incident and resolved the problem.

Image copyright PA Media Image caption The outage caused "enormous disruption", said Business Secretary Andrea Leadsom

Energy regulator Ofgem has already demanded an "urgent detailed report" into what went wrong and could take enforcement action, including a fine.

And the National Grid has promised it will "learn the lessons" - but added its systems were not to blame.

The outage happened after problems at two power stations - the gas-fired station at Little Barford in Bedfordshire at 16:58 BST and then at Hornsea offshore wind farm two minutes later.

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 17:40 BST on Friday but there was a knock-on effect for some train services, which continued to be disrupted into Saturday.

National Grid's director of operations Duncan Burt said he did not believe that a cyber-attack or unpredictable wind power generation was to blame.

Speaking on BBC Radio 4's Today programme on Saturday, Mr Burt acknowledged the "immense disruption" the blackout had caused.

He said the near-simultaneous loss of two generators was more than the grid was routinely prepared for, prompting automatic safety systems to shut off power to some places.

"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," he said.

Media playback is unsupported on your device Media caption The National Grid's operations director explains why nearly one million people lost power on Friday

But he said the industry needed to examine whether these safety systems were set up correctly to have "minimal impact" on people's daily lives.

Shadow business and energy secretary Rebecca Long Bailey 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.

Image copyright PA Media Image caption All services in and out of King's Cross station were suspended during Friday's rush hour

Police were called to help travellers during the huge disruption on the railways on Friday, with delayed passengers stranded for hours.

Disruption continued into Saturday for some routes, with services to and from King's Cross station in London particularly badly hit.

Passenger Dayna McAlpine told BBC Radio 5 Live her train took nearly 13 hours to reach London King's Cross from Edinburgh - a journey which would normally take less than five hours.

"By hour seven things were starting to get pretty tense," she said. "People were threatening to self-evacuate off the train... Food ran out about five hours ago."

Image copyright Lily Winnan Image caption Passengers on a train near Kentish Town station got off and began walking along the tracks

Image copyright PA Media

At the worst point of the power cut, about 500,000 people were affected in Western Power Distribution's area - including 44,500 customers in Wales - while 110,000 Northern Powergrid customers also lost power.

In London and south-east England, 300,000 people were affected, UK Power Networks said, and another 26,000 customers were without power in north-west England.

Northern Powergrid said the problems had affected Newcastle Airport and the metro system in the city.

At Ipswich Hospital, a back-up generator which was supposed to supply power to outpatient areas did not work after the power cut, causing problems for 15 minutes before power was restored.