The power cut which brought chaos to large parts of Britain was caused in part by an over-reliance on wind energy, experts have warned.

The Mail on Sunday can also reveal there have been two other sharp drops in energy supply in the past three months alone – as a leading expert warned that blackouts will become ‘increasingly frequent’.

With the country still reeling from the power outage, which hit almost a million people on Friday afternoon resulting in widespread disruption to trains and roads, the National Grid pointed the finger of blame at the two foreign companies which own the affected power stations.

However, one of the firms in turn called for a probe by the National Grid and regulator Ofgem to find out where responsibility lies.

People walking in complete darkness at Clapham Junction station in London during a power cut on Friday. There were widespread power outages across the country after two generators went down

An office block in Newcastle was left in the dark as its electricity cut out during the power outage

Traffic lights went dark at a busy junction on Northcote Road near Clapham Junction, south west London (pictured)

King's Cross Station in London was evacuated following the power cut and commuters were forbidden from passing through the ticket gates

Amid other developments:

Ofgem has warned the National Grid it faces a fine of up to ten per cent of its turnover after the power failure.

Bosses at Ipswich Hospital are investigating why back-up generators failed.

Renewables UK, which promotes wind power in the EU, boasted on its Twitter account that wind was generating 47.6 per cent of our electricity – just hours before the blackout occurred. The National Grid then retweeted the message with the words ‘It’s Wind o’clock’.

The power cut across England and Wales was caused by two power stations shutting down almost simultaneously just before 5pm.

A gas-fired power station in Little Barford, Bedfordshire, owned by German company RWE, was the first to fail, at 4.53pm. Within minutes, the Hornsea offshore wind farm in the North Sea, run by Denmark’s Orsted, also ‘lost load’ – meaning the turbines were moving but power wasn’t reaching the grid.

The National Grid was unable to cope with the loss of power, forcing it to cut demand in large areas to protect the rest of the system.

Renewables UK, which promotes wind power in the EU, boasted on its Twitter account that wind was generating 47.6 per cent of our electricity – just hours before the blackout occurred

The escalators at King's Cross station stopped working following the power cut and commuters were prevented from entering the station

People walking through Clapham Junction station in London during a power cut. Many appeared to emerge from darkness, following the loss of power at the station

A motorist gets out of his vehicle to direct traffic after a power cut in Gateshead led to traffic lights failing

National Grid boss is ridiculed after insisting 'the system worked really well' despite blackout chaos It was an outrageous statement worthy of dictator Saddam Hussein’s propaganda chief, nicknamed ‘Comical Ali’ for his laughable distortions of the truth during the Iraq War. The day after the power went off all over Britain, causing widespread chaos, National Grid director of operations Duncan Burt yesterday insisted: ‘We think the system worked really well. What we saw was an exceptional event.’ National Grid director of operations Duncan Burt (left) insisted 'the system worked well' after the power cut. It was an outrageous statement worthy of dictator Saddam Hussein’s propaganda chief (right) He told Radio 4’s Today programme: ‘We think that the protection systems across the generators and the network worked well to secure and keep the grid safe… to make sure we preserved power for the vast majority of the country.’ He was speaking after the power cuts halted trains, shut down traffic lights and left nearly a million people without power. Mr Burt said the ‘near-simultaneous’ loss of two stations disconnecting was more strain that the grid could deal with, triggering automatic safety systems to shut off power to some areas. He acknowledged the ‘immense disruption’ the blackout had caused and said the industry needed to examine if the safety systems were set up to have ‘minimal impact’ on people’s lives. He said lessons would be learnt. Saddam’s Information Minister, Muhammad Saeed al-Sahhaf, was dubbed Comical Ali for his denial of reality during the Coalition invasion, in one instance claiming that US soldiers were committing suicide ‘by the hundreds’ just as the regime was crumbling. By Jonathan Bucks for The Mail on Sunday Advertisement

The blackout lasted for an hour, leading to cancellations and delays on at least 14 rail networks and stopping road traffic lights from working. Astonishingly, the National Grid has insisted its own systems had ‘worked well’.

Ofgem has already threatened the company with a possible fine and yesterday said it had received a summary report from the company into the causes of the failures.

RWE has also called for an investigation into the ‘wider system issues’, adding such failures ‘are not uncommon in power stations’.

One expert, Jeremy Nicholson, of energy firm Alfa, said he feared there might be worse to come because of Britain’s growing use of renewable energy.

‘Has the National Grid been taking the actions that are necessary to keep the lights on when there’s not much conventional generation on the system?’ he added. ‘This is going to be increasingly frequent in future as our dependence on wind and solar grows.’

Data seen by The Mail on Sunday has also revealed there were two significant drops in the stability of the UK’s electricity supply in May and June. Last year, the UK generated 33 per cent of its electricity from renewable energy sources, up from 6.5 per cent in 2010.

Energy experts said using coal and gas power stations makes it easier to cope with fluctuations and outages because they hold more latent capacity – known as ‘inertia’ – in their systems.

Mr Nicholson said of the two incidents earlier this year: ‘It wasn’t quite outside of the operational range but if it had been slightly tougher and one or two other things had gone wrong then we would have been in similar territory.

‘Because there was so much wind and solar on the system, there was very little conventional generation – coal and gas – which provides inertia that helps stabilise the frequency of the grid. The system should have coped. So when National Grid say things like, “the system worked” and that the power blackouts didn’t spread, that’s like a doctor saying the operation was a success but the patient died. It’s not much comfort to consumers.’

The last major power cut came in 2008 when hundreds of thousands of homes were affected after two power stations similarly went off-line within minutes of each other.

Friday’s blackout affected about 300,000 UK Power Networks customers in London and the South East between 4.53pm and 5.21pm.

Western Power Distribution said that 500,000 customers in the Midlands, South West and Wales were left without power until after 6pm.

Northern Powergrid had 110,000 affected customers and Electricity North West another 26,000.

At Ipswich Hospital, journalist Vikki Irwin said her seriously ill mother was about to have a CT scan when the power failed, leaving her stuck for 15 minutes as a lift didn’t work. No patients were harmed.

A National Grid spokesman said: ‘We appreciate the disruption and investigations have continued to better understand the situation.’

We're like Venezuela - next time the lights could be out for weeks: Political analyst RICHARD NORTH on the power cut that sent Britain in meltdown

By Richard North for The Mail on Sunday

The wind farm industry was bursting with good news on Friday. Wind was generating as much as 47.6 per cent of our electricity, announced Renewables UK, a body which promotes wind power in the EU. ‘A new wind record!’ it exclaimed.

Shortly afterwards, Britain’s electricity system went down in a catastrophic failure that deprived nearly a million people of power, stranded thousands of rail passengers and caused chaos on London roads.

The blackout was little short of a disgrace. Accidental power cuts on this scale should never happen in modern, developed countries, particularly not when computers are now so integral to life.

This is the sort of thing we expect in train-wreck economies such as Venezuela. Yet not only did this ‘outage’ take place in Britain, it will almost certainly happen again and potentially on a more devastating scale, leaving whole areas of the country without power for weeks.

At 5pm on Friday the Hornsea Offshore wind farm in the North Sea (pictured) was knocked offline. The national Grid tried to increase power to the network from other generators but were forced to suspend supplies to protect the network

A chef in Cornwall stands in the dark as machines and lights were switched off during the mass outage yesterday. It has impacted the Fistral Beach Boardmasters surf competition

Part of the problem is the obsession with ‘renewables’ such as solar and, particularly in Britain, wind power. We ignore how patchy their contribution is. The wind doesn’t always blow.

Relentless green optimism, moreover, has helped divert us from the truth – that there has been no coherent planning for electricity since the Second World War. Our entire national system is dangerously fragile and getting worse.

In the rush to wind, other, more reliable sources of electricity, including local generation schemes have been ignored – as has the rackety state of the National Grid which now needs billions of pounds in additional investment.

Friday's disaster began with the failure of a relatively small gas plant at Little Barford in St Neots, Cambridgeshire. Two minutes later, the vast Hornsea offshore wind farm in the North Sea failed. Together, they were generating power equivalent to less than one 20th of the total demand. Yet such is the fragility of our infrastructure, it caused a crisis in the National Grid, the central power distribution system.

Things could have been a lot worse. The great danger at such times is what is known as a ‘cascade failure’, such as a 2003 power cut in the United States and Canada, which wiped out nearly 80 per cent of the electricity supply in the North-Eastern states. It affected more than 50 million people, with operators taking two days to restore supplies. Some areas went without power for two weeks.

In Britain, we should never have a situation where the failure of a gas power station near a sleepy town, followed by a problem at an offshore wind farm causes ‘outages’ in London – much less nationwide.

But even on good days, the National Grid performs poorly. That it works at all is a daily miracle, achieved by the people who manage the system. It is set to get worse. In the post-war years, coal-fired power stations were the mainstay. Even as late as 2012, coal was supplying more than half of our daily requirements.

Now, under a policy regime aimed at reducing global warming, coal has been abandoned, replaced by more distant and scattered packages of renewables, mainly wind farms – some small, some gigantic. These wind farms have put the network under even greater stress.

A gas-fired power station (pictured) in Little Barford, Bedfordshire, owned by German company RWE, was the first to fail, at 4.53pm

Then, there is the near-insoluble problem of variability, where wind can be pumping power into the system one moment, and, minutes later, producing nothing. Hornsea is designed to be six times bigger than at present – and the bigger it gets, the worse the problems will be. In an attempt to cope with this, the National Grid has helped create a nationwide network of diesel generator farms to provide back-up for when wind fails. On Friday, that system failed as well.

It is worth remembering how things worked in the past, when generating electricity was a more local matter. At one time or another, there have been no fewer than 18 power stations on the banks of the Thames, from Tilbury to Kingston, each serving their own localities. From 1905 until 2002, the London Underground had its own dedicated power station in Fulham, supplying underground trains, trams and trolley buses. It was only in the mid-1920s that Britain started connecting up this fragmented system.

But it was after the War that the real change came, with the development of gigantic coal-fired stations, augmented by nuclear plants on coastal sites as far apart as Kent, Cumbria and Anglesey.

Among them was huge, coal-fired Drax power station in Yorkshire, originally conceived in 1962. Today, in these politically correct times, it has been converted to so-called biomass, consisting mainly of chopped-up trees shipped over at great expense from Canada, where whole forests are stripped to keep this behemoth supplied.

As a result, the National Grid, which had barely existed before the war, found itself sending high-voltage electricity via a network of pylons over hundreds of miles. (It is estimated that up to ten per cent of the generated power is lost in heating the transmission cables, twice the amount that brought down the system on Friday.)

Commuters are taken off a Thameslink train on Friday following the power outage, which caused major disruption across the country

This is something for which our national supply network was never designed or developed, and why it is now so vulnerable. Whatever your views on renewables, it is absolute folly to invest in wind without investing in the infrastructure needed to make it work.

Britain's obsession with vast size is another part of Friday’s blackout. Power can and should be generated more locally and on a smaller scale, as in the small German city of Freiburg. It produces about 50 per cent of its electricity with a system known as combined heat and power from a mixture of natural gas, refuse and gas extracted from sewage.

It has 14 large-scale and about 90 small-scale CHP plants, which provide both heating and electricity. The system is pretty much immune to national power cuts.

And instead of giant and costly nuclear plants, we could learn from Rolls-Royce – a leader in the field – and develop ‘mini-nukes’ – factory-built plants based on nuclear submarine technology, which can be installed close to demand.

Our Prime Minister need look no further than his own residence to see that local works. Twenty-three Whitehall buildings are supplied with heat and power from a private power station in the bowels of the Ministry of Defence. It was fully commissioned in 2005, just as Tony Blair was working up an energy policy that threatens to turn the lights out all over the UK.

So Mr Johnson can count himself as fortunate when, as will happen, the nation once again shivers in darkness. The lights at 10 Downing Street will remain bright, his radiators warm. Would that the rest of us might be so lucky.