On the afternoon of June 23, many were enjoying the start of a heatwave that would take temperatures up to 37C, surpassing the June record set in the scorching summer of 1976.
As we sweated, most of the country was blissfully unaware that a potentially catastrophic energy crisis was unfolding.
It emerged this week that on that baking Tuesday, we came close to suffering an event as dramatic as the blackout that occurred in Spain and Portugal in 2025 when trains stopped, industry and commerce were suspended, and hospitals were forced to switch to emergency backup supplies to prevent patients from dying.
Control room engineers at the National Energy System Operator (Neso) the little-known government body responsible for balancing Britain’s electricity supply and demand, were panicking. The grid’s frequency had destabilised and dropped below Neso’s strict operating limit, threatening widespread blackouts.
Yet it was alleged this week that bosses were less concerned by the system failures and more by the reputational impact of the public discovering that the grid was not being run securely. This allegedly involved ordering staff not to keep records of operational decisions to ensure there was no paper trail, in case they might have to be revealed in a Freedom of Information request.
Meanwhile, members of Neso’s corporate affairs team, who manage media and government relations, are said to have interfered in the control room, telling operators what to do to protect the body’s reputation.
This unbelievable tale was revealed by Shadow Energy Secretary Claire Coutinho, after she was approached by several whistleblowers. ‘They are coming to me because they are worried that the grid is becoming unmanageable and they do not have faith that their concerns are being taken seriously’, she said.
Coutinho further revealed that at a meeting on Monday, the Chief Executive, Fintan Slye, told staff that allegations that grid security standards were breached were false. What’s worse, the whistleblowers were openly criticised by senior management for letting the company down. The Government now confirms there is an independent inquiry into what happened on June 23.
The National Energy System Operator (Neso) is a company with a single shareholder: the Secretary of State for Energy Security and Net Zero, currently Ed Miliband
The UK came close to suffering an event as dramatic as the blackout that occurred in Spain and Portugal in 2025 when trains stopped and hospitals were forced to switch to backup supplies
Before this week’s events, few had heard of Neso. Fewer still appreciated how finely balanced Britain’s electricity system is, or how difficult it has become to keep supply and demand in equilibrium as Ed Miliband pushes towards his target of a carbon-free electricity grid by 2030.
Neso was created under the previous Conservative government’s Energy Act 2023, taking over many of the functions previously carried out by the private company, National Grid ESO, with two principal objectives: to ensure the lights stay on and to prepare the national grid for the transition to Net Zero.
Based in an unassuming office block in Warwick, Neso employs around 2,200 people. According to its own calculations, it costs the average household £6.46 a year through energy bills. Yet its 2024/25 annual report also recorded a loss of £409 million, which will have had to be covered by taxpayers. While Neso manages our energy system, it owns little of it. The pylons, substations and infrastructure remain in private hands. Nor does it own the country’s power stations, wind farms or solar farms, all of which are also owned and operated privately. Instead, Neso acts as a glue holding together this patchwork of private assets, coordinating them into what is supposed to function as a single, seamless network.
Although often described as ‘independent’ of government, Neso is a company with a single shareholder: the Secretary of State for Energy Security and Net Zero, currently Ed Miliband.
In other words, it is a public sector body, although the pay packages of its senior staff might not suggest it. In 2024/25, chief executive Slye received a basic salary of £288,167 – more than £100,000 higher than the Prime Minister’s. Once pension contributions and performance-related payments were included, his total remuneration reached £773,650. Chief operating officer Kayte O’Neill received £564,311, while chief financial officer Charlie Pate was paid £317,451.
If you’re wondering what Neso’s 2,200 staff do all day, look no further than the interactive game on its website, which invites visitors to ‘run the national grid yourself’. Even this simplified version conveys the extraordinary complexity of the task. At every moment, electricity supply has to be matched almost perfectly with demand. In front of you is a dial showing the frequency at which the grid is operating. Britain’s mains electricity uses alternating current, meaning the flow of electrons through the wires continually reverses direction. The number of times this happens each second is measured in hertz (Hz).
The grid must be kept as close as possible to 50Hz. In real life, the acceptable operating range is even tighter: within a range of 0.4 per cent either side.
If too much electricity is generated relative to demand, the frequency rises above 50Hz. If too little, it falls below. Either scenario risks damaging equipment and, in the worst case, triggering widespread power outages.
Neso’s game gives players a range of tools to keep the system in balance. You can buy more electricity from gas-fired, nuclear or biomass power stations (the latter controversially fuelled by imported wood pellets). You can import or export electricity through subsea cables or charge and discharge batteries and hydroelectric plants.
What you cannot do – and this illustrates why running the grid is becoming harder – is simply manipulate renewable generation at will. ‘You can’t control renewables’, the game explains (in real life you can turn them off but not up if there’s no sun or wind). ‘But keep an eye on the weather forecast so you can adjust the other energy sources accordingly.’
Therein lies the problem. As Britain moves towards a carbon-free electricity system, around 80 per cent of generation is expected to come from wind and solar. The greater the share supplied by weather-dependent sources, the smaller the proportion of the system that grid operators can directly control when balancing supply and demand.
Britain’s grid was designed around coal power stations in the Midlands and South Yorkshire – and even Ed Miliband has downgraded his ambition for a carbon-free grid by 2030
With a heatwave anticipated, Neso had expected a surge in demand for electricity-guzzling air con units while the excessive heat would also cause problems for solar farms
The first time I played Neso’s game, I crashed the grid within a couple of minutes. On the second, I managed to keep the lights on until the end of my shift, but only just. The biggest hiccup came when I was suddenly informed that a heatwave had led to all solar farms having to be switched off to prevent the heat from damaging them. This, coincidentally, is close to what seems to have happened on June 23.
According to Kathryn Porter, who runs independent energy consultancy Watt-Logic, on several occasions that day, the frequency of the grid dropped dangerously below 50Hz, suggesting that not enough power was being supplied. This was despite Neso issuing a ‘margin call’ in advance: a request for help put out to electricity generators when there is a predicted imbalance between supply and demand.
With a heatwave anticipated, Neso expected a surge in demand for electricity-guzzling air con units. At the same time, the excessive heat was expected to cause problems for solar farms.
To absorb sudden changes in frequency and voltage, our energy grid relies on buffers in the form of heavy spinning turbines. But these turbines mostly operate in traditional power plants (such as coal, gas, or nuclear).
So when solar generation dominates, as it did on the day the Spanish grid failed, there are too few of these ‘buffering’ turbines working to cushion the system against sudden disturbances.
At the time of Spain’s blackout, solar was supplying around 58 per cent of its electricity. We’ll have to wait to see what Neso’s independent inquiry turns up about last month’s events. But if it really is struggling to balance the grid now, what happens when the system is even more heavily dependent on wind and solar?
The trouble is we have a grid which was designed around a clutch of coal-fired power stations in the Midlands and South Yorkshire. It is far less suited to a system powered by dispersed, weather-dependent renewables.
Ed Miliband has already quietly downgraded his ambition for a carbon-free grid by 2030 to one which is 95 per cent carbon-free. In 2024, Neso declared that this slightly watered-down target was possible to reach, estimating the required grid upgrades would cost £58 billion. Yet, by June this year, that estimate had risen to £89 billion – more than £1,000 for every man, woman and child in Britain. And that is only the cost of upgrading the grid, not building large-scale wind and solar farms, nor the cost imposed on housebuilders, whom Miliband has ordered to install solar panels on new homes, even where roofs may be heavily shaded. A lot of the cost is down to Miliband’s rush to transition to renewables. The previous Conservative government had already set a target of decarbonising the electricity system by 2035, but Miliband judged that too slow.
‘If a target is set to do the practically impossible in around 60 months, then the logical consequence is that it will cost whatever it costs,’ according to Sir Dieter Helm, Professor of Economic Policy at the University of Oxford. Others argue that a Net Zero electricity system by 2030 is unattainable at any price. According to Gary Smith, general secretary of the GMB union – not usually a critic of the Labour government – there simply isn’t enough specialist equipment in the world to build the offshore wind farms needed to meet the target.
There is another nasty contained within Neso’s plans.
To achieve a 95 per cent carbon-free electricity system by 2030, it says Britain will require between 10 and 12 gigawatts of ‘consumer-led flexibility‘.
That means encouraging – or forcing – people to reduce their energy use at peak times, perhaps through surges in the electricity price when the supply is struggling to keep up with demand.
One way or another – through blackouts or price gouging – Neso will make sure it is customers paying the price of the transition to a carbon-free grid.
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