THOUSANDS of desperate passengers were stranded on trains for more than six hours in the dark last night as a UK-wide power cut wreaked havoc on trains, Tubes and roads.

A million people across the UK were plunged into darkness after two National Grid generators spectacularly failed, with large parts of London, the South East, Liverpool, Glasgow, Wales, Gloucestershire and Manchester all without power.

23 Train workers rescue passengers from a stranded train after six hours near Hatfield, Herts Credit: Steve Shaw

23 Passengers were forced to walk on the tracks after their train from Moorgate was evacuated Credit: @SpartanStathi

23 London Underground passengers walk through a tunnel in the dark after a power failure crippled the UK

Commuters described "apocalyptic" scenes when power failed around 5pm - even knocking out traffic lights in some areas.

Trains were stuck on Thameslink and the East Coast main line, with delays and cancellations continuing all evening.

Witnesses described "pandemonium" as cops were called to break up fights and passengers were forced to pee out of windows.

Christopher Lovell tweeted: "Been sat on a train outside Hatfield for 4.5 hours now.

"People have been p*****g out of the drivers door as there are no toilets.

"Completely unacceptable, multiple opportunities to evacuate the train while it was still daylight."

Vicki Hamilton said: "Over 4 hours later and still stuck on this @TLRailUK train with no water, no food and no power!"

Our video shows passengers being rescued after six hours stuck between Hatfield and Welham Green, Herts - as the driver says they are finally getting off this "nightmare train".

One traveller on board told The Sun Online: "It was pitch black, toilets were overflowing, people were shouting and children crying.

"It was pandemonium. After about five hours the police came to break up fights.

"People were smoking in the toilets and then squaring up to other people who objected.

"Passengers were on the point of revolt."

He said a diesel train was eventually brought alongside and workers helped them across the track.

After seven hours they reached Hatfield station and were put on buses to London.

He added: "A policeman told me they'd evacuated ten trains, and there were 50 trains stuck because of the power cut."

Other pictures show passengers walking on tracks in North London and in a London Underground tunnel.

Major power failures across large parts of the UK hit trains, airports and traffic lights

23 Police boarded a stranded train 'to break up fights' on the East Coast main line, witnesses said Credit: Steve Shaw

23 Passengers were taken off the train after a six-hour 'nightmare' Credit: Steve Shaw

23 They were given water after finally reaching Hatfield on a second train Credit: Steve Shaw

Meanwhile at King's Cross 1,000 people were shut outside and others slept on the floor inside as train companies told ticket holders: "Do not attempt to travel."

Euston Station was also evacuated and people were stuck underground on the Victoria Line at the height of rush-hour.

Harriet Jackson 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."

Newcastle Airport also suffered a blackout. Scott McKenzie, 31, from Cardiff, said: "We were literally plunged into darkness and people were using their phones as torches to see and get around."

It was the first major outage since 500,000 lost power in London in 2003.

Western Power Distrubiton, which serves the Midlands, South West and Wales, said 500,000 people were affected.

More than 100,000 homes in Devon were left without power, and around 300,000 UK Power Networks customers were affected in London and the South East.

Northern Powergrid, which serves Yorkshire and the North East, said 110,000 customers lost power while Electricity North West said a further 26,000 customers were affected.

Later the National Grid said power had been "restored" after two generators failed, but energy watchdog Ofgem has called for an "urgent detailed report" so it can investigate.

A spokesman said: "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."

23 Commuters stuck outside Green Park station in London Credit: @immayo1

23 Passengers stuck in the dark on the Victoria Line Credit: @AislingJane_

23 Passengers lying on the ground in the middle of King's Cross Credit: PA:Press Association

23 Hundreds were refused entry into King's Cross station as trains were halted Credit: PA:Press Association

23 Shoppers filmed in the dark at Waitrose in Buckhurst Hill, Essex

23 Emergency lights guide commuters who were plunged into darkness at rush hour at Clapham Junction Credit: PA:Press Association

23 Huge crowds in the blackout at Clapham Credit: @JoeWelstead

23 Traffic lights went down in Northcote Road near Clapham Junction Credit: PA:Press Association

23 A motorist gets out of his car to direct traffic after a power cut paralysed the lights failing on the A167 in Low Fell, Gateshead Credit: North News and Pictures

23 Electricity supplies were knocked out across large swathes of Cornwall, like in this restaurant Credit: Splash News

Tube passengers in London reportedly collapsed due to heat exhaustion after a Victoria Line train was stuck between Oxford Circus and Green Park for 25 minutes.

Meanwhile, cops were filmed boarding a train stranded at Potters Bar station in North London after the power went out to help with crowd control.

A British Transport Police (BTP) spokesman said: "We currently have BTP officers assisting at several stations owing to current disruption caused by power issues."

Network Rail said power outages sent their signals down, resulting in cancellations and delays in the Newport, Gloucester, Ashford, Bristol, Eastbourne, Hastings, Three Bridges and Exeter areas.

Rail operator Thameslink said many of its trains were "at a stand".

Commuters in Liverpool and Stockport in Cheshire also complained of power outages.

Meanwhile, passengers reported being "thrown off" an escalator after it suddenly stopped in Bradford, West Yorks.

As homes across London were plunged into darkness - sending mobile phones and the internet down - locals wrote: "It's scary as hell".

The drop in power also affected traffic lights in the capital, Transport for London confirmed.

It said: "Due to a large scale National Grid failure there is a power cut in the London and South East areas, meaning that some traffic lights are down.

"Please be very cautious on the roads!"

Last night there were reports the outage was caused by a failure of one gas power station and a major wind farm at the same time.

National Grid confirmed at around 6.40pm that the issue had been "resolved" - but the knock-on disruption lasted hours.

UK Power Networks said: "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."

The outage came as the country is lashed by heavy rain and thunderstorms - with severe weather warnings in place for almost all of the UK.

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National Rail Enquiries said: "Power supply problems are currently causing disruption to a large number of train services. Information screens in some areas are also affected."

It added: "The UK power network has failed in the large parts of London and the South East. This has prevented trains across the Great Northern network and between Farringdon and Bedford from being able to take power and as a result, most trains are currently at a stand."

It's the second day of travel chaos for commuters in London as thousands were left stranded in Euston and Marylebone because of signal failures.

How to claim compensation for unplanned power cuts IF you've been affected by a power cut then you could be owed cash. Here's all the details. If the power cut was caused by bad weather, you should be paid compensation without having to claim. But if you don’t receive the compensation you can claim it yourself by contacting your network provider. How much can you get? The amount of compensation you can get depends on how many homes were affected by the power cut, how long it last and whether it was caused by bad weather. You can contact your network operator to find out how many homes were affected. Compensation ranges from £35 up to a maximum of £700. How to claim You should be paid within 10 days of claiming, or if the power cut was caused by bad weather, you should be paid as soon as is reasonable. If you’re not paid within these timescales, you can get a further payment of £30 for late payment. If the network tells you that you’re not eligible for compensation, and you disagree, you should complain directly to it. Use its complaints procedure, which will be on its website. If you’re not satisfied with the response to your complaint, you can complain to the energy ombudsman.

23 Huge crowds at Victoria station as the power cut shuts down parts of the tube Credit: Raj Patel - Clickshot Memories

23 King's Cross was packed full of stranded commuters

23 There were delays to trains and the Tube Credit: Raj Patel - Clickshot Memories

23 There were huge queues at St Pancras Credit: @rosiehunnam

23 Commuters walk on the tracks after getting off stranded trains Credit: @GFEllsworth

23 A LNER staff member pushes a trolley of bottled water at Peterborough station to passengers on a delayed train Credit: PA:Press Association

23 Ticket machines out of order at Clapham Junction station Credit: PA:Press Association

Love being stuck on the Victoria line during a power surge and turned into a human sweat marinade pic.twitter.com/6thbc0bMQJ — Suleman (@namelus_) August 9, 2019

Fill her up........ gotta love a power cut pic.twitter.com/huQWxsOr8f — Flaxtonboy© (@Flaxtonboy1) August 9, 2019

A significant drop in generation this afternoon caused a major drop in frequency leading to power cuts across the country. Our fleet responded as expected helping stabilise the grid. Upside Energy Ltd #powercut @upsideenergy pic.twitter.com/k3RFRV9Blw — Devrim Celal (@dcelal) August 9, 2019

4.30 train from Moorgate. 6.59pm and been stuck on the train between Alex Park and New Southgate. Train being evacuated, waking on tracks back to AP. Beautiful pic.twitter.com/B0NQZNsvVw — Stathi Marneros (@SpartanStathi) August 9, 2019

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