- Video report by ITV News reporter Angus Walker
Rail passengers left stranded by a major power cut which stopped trains have been urged to claim compensation by a leading watchdog.
Network Rail passengers were marooned after the loss of power affected trains across the country, as more than one million people were left without electricity following outages at two power stations.
Issues on the national grid led to power being lost to signalling in areas including Kent, Gloucestershire, Devon and East Sussex.
At London's King's Cross station, passengers were filmed forcing their ways through the barriers in an attempt to get on to the first northbound service after services were stopped for several hours.
The situation was labelled "absolute mayhem" with some passengers sitting or lying in the station concourse surrounded by bags and luggage, while others crowded outside.
More than 1,000 passengers appeared to be stranded at the station as main entrances were sealed off.
David Sidebottom, director of independent transport user watchdog Transport Focus, said on Saturday: "The severe disruption to services that followed power outages yesterday evening made routine journeys home or away for the weekend impossible for lots of rail passengers."
He said the watchdog recognised the efforts made under "extreme circumstances" to keep passengers safe and help them complete essential journeys.
"Any passengers who heeded advice not to travel should claim delay repay compensation in order to get their money back, including those using a season ticket," he added.
"People whose journey was severely disrupted should also keep receipts for all unexpected costs that arose from their efforts to complete their journeys yesterday, and contact their train operator to claim not just for their delay but any additional expenses they incurred."
It comes after energy watchdog Ofgem demanded an urgent report from National Grid.
The energy regulator said in a statement: "Ofgem understands the frustration this power cut has caused consumers.
"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.
"This could include enforcement action."
National Grid has described the loss of power across the country on Friday as an "incredibly rare event" and said there will be a a "detailed technical report".
- Rush hour chaos as trains grind to halt
Commuters were left stranded during the sudden power outage.
Blackouts were reported just after 5pm in London and the South East, the South-West, Wales, as well as the Midlands, the North-West and the North East of England.
The National Grid Electricity System Operator said issues with two generators caused the loss of power.
The operator said shortly after 6.30pm the electricity issue was "resolved", however travel disruption continued into the night.
On passenger, Joshua Carr, was travelling from Edinburgh to London when the powercut hit. He was told by the LNER at Newcastle of the outage. He managed to get to York, but was to change trains there.
He took a photo of the delay on the train, showing more than four hours.
Mr Carr got to Stevenage but the train stalled just outside the station. He finally arrived to Kings Cross at 1.45am - four hours after he should have done.
He complimented the train company on the "useful and polite" staff. He said he was offered a taxi but was told it would be another 80 minutes.
The Department for Transport said: "Today's power outage has had knock on impacts on travel.
"We're working hard with Network Rail and others to ensure systems are up and running as quickly as possible, so that everyone can complete their journeys safely."
- How have people reacted to the power cut?
One passenger at King's Cross who was stuck in the Underground with her family told ITV News: "We got stuck on the underground. The power failed, the electric went and they had to restart the engine.
"It was very hot and sweaty for about 20 minutes on the Victoria Line."
Another commuter said: "It's been nothing but delays shown up on the board and cancellations, so I thought I'd hang about and see what happens but unfortunately now we are being told to leave the station."
Traveller Zoe Hebblethwaite has described the situation outside Kings Cross station as "absolute mayhem" after the transport hub was closed due to the power issues.
The 23-year-old had been stuck for almost two hours when she spoke to PA, having arrived at the station at 5.30pm before being told to leave until further notice.
"They have closed doors of the station - no power whatsoever," she said.
"Outside Kings Cross Station is absolute mayhem nobody knows anything nobody can find an assistant to speak to at this point.
"No commuters are allowed in... There is so much confusion."
The legal secretary from Pontefract, West Yorkshire, said she had no other means of reaching the London North Eastern Railway and she is waiting to see if the problem will be resolved by the end of Friday night.
Scott McKenzie was travelling through Newcastle Airport when the power cut out for around 15 minutes, in what he was told by officials was "due to a wider problem in the region".
"It was a bit worrying to start - more so because various alarms were going off and staff clearly didn't quite know what was going on either," the 31-year-old from Cardiff said.
"Some of the spaces in the airport have little daylight - we were literally plunged into darkness and people were using their phones as torches to see and get around."
Mr McKenzie said the problem at the airport "seems to have been resolved" and Newcastle Airport said it is aware of the power issues but flights have not been disrupted.
Harriet Jackson described an "apocalyptic" scene when she witnessed the power outage causing traffic lights to cut out on Northcote Road in Battersea, London, after leaving Clapham Junction train station at around 5pm.
"(I) realised that nothing was open and there was hardly any phone signal," the 26-year-old said.
"All the traffic lights were down, but there were no police present, which meant it was dangerous to cross - cars weren't stopping either.
"It was like witnessing something out of an apocalyptic film.
"No one knew what was going on and, given it's a Friday afternoon, it's the last thing you want to encounter."
Christopher Connor, 30, said the cut to power in North West England disrupted lights and phone lines near his home in Cheadle Hulme, Stockport.
He said alarms were also set off by the temporary outage and traffic lights stopped working entirely.
"The traffic was running smoothly though a little more haphazard than normally," he said
- How badly have rails and roads been affected?
The drop in power is still affecting travel.
Train services across England and Wales are facing reported delays and cancellations.
Many passengers were sat or lying down in London's King's Cross Station concourse surrounded by bags and luggage, while others crowded outside.
Main entrances were sealed off and closely watched by staff, but other doors at the opposite side of the station remained open.
Police officers were unable to say when services would resume and information boards inside only said services were "subject to severe delays and short-notice cancellations".
More than 1,000 passengers appeared to be stranded at the station, which serves the East Coast Main Line and Scotland.
London North Eastern Railway (LNER) had warned customers not to travel as services into and out of King's Cross were suspended but lines have reopened now, albeit with delays.
A Network Rail spokeswoman said: "There was a power surge on the national grid this evening which means we lost power to all our signalling over a wide area, including the Newport, Gloucester, Ashford, Bristol, Eastbourne, Hastings, Three Bridges and Exeter areas.
"All trains were stopped while our back-up signalling system started up."
Traffic lights in the capital are also experiencing some problems and the Victoria Line on the London Underground is suspended, Transport for London confirmed.
Police could be forced to man busy junctions where traffic lights have been shut down, Transport for London said.
A TfL spokeswoman said some traffic lights are "not working" but the scale of the problem is not yet known.
Police officers could be called in to "manage the busy junctions, to physically manage them themselves", she said.
"We're just assessing how many traffic signals are out."
British Transport Police has said its officers are assisting at train stations disrupted by the power cut.
Thameslink, Southern and Gatwick Express - all serving lines into and out of London - are facing delays and cancellations.
Rail operator Thameslink said many of its trains were "at a stand".
A tweet said: "The power network has failed in the large parts of London and the South East. This has prevented our trains between Farringdon and Bedford from being able to take power and as a result, most of our trains are currently at a stand."
- What was the scope of the power cut?
Around one million people were affected by the power cut.
UK Power Networks tweeted on Friday evening: "We're aware of a power cut affecting large parts of London and South East.
"We believe this is due to a failure on National Grid's network, which is affecting our customers."
Western Power Distribution shared a similar message, and said they are in the process of restoring power to customers.
A spokeswoman for Northern Powergrid said 110,000 of its customers lost power between around 5.10pm and 6pm.
She said the problem was with the National Grid's transmission network, which distributes high voltage energy from power stations across the UK.
The power cuts were "quite spread apart, (which is) quite unusual", the spokeswoman said.
Western Power Distribution said around 500,000 people were affected in the Midlands, South West and Wales, with power restored to them all shortly after 6pm.
In the South-East, East of England and London, around 300,000 UK Power Networks customers were hit by the power cut, a spokeswoman said.
At least 26,000 people were without power in the North West of England, Electricity North West said.
A spokesman said the outage was spread from Penrith, in Cumbria, to Stockport, in Greater Manchester.
Cheshire Police said they were aware of a power cut in the Ellesmere Port area.
In neighbouring Liverpool, Merseyrail said all services on the Wirral Line in Merseyside are suspended.