The National Energy System Operator (Neso), a government body responsible for balancing Britain's electricity supply and demand, is facing accusations of covering up the near-collapse of the national grid during a severe heatwave on June 23. Whistleblowers have reportedly approached Shadow Energy Secretary Claire Coutinho, alleging that Neso bosses were more concerned with reputational damage than system failures, and that staff were instructed not to keep records of operational decisions to avoid a paper trail.
On the afternoon of June 23, as temperatures reached up to 37C, Neso control room engineers reportedly experienced a destabilization of the grid's frequency, dropping below its strict operating limit and threatening widespread blackouts. This situation is being compared to the 2025 blackout in Spain and Portugal, which caused significant disruption to transport, industry, and essential services. Coutinho stated that whistleblowers are concerned about the manageability of the grid and a lack of faith that their concerns are being taken seriously.
Neso, established under the Energy Act 2023, has the dual objectives of ensuring a stable electricity supply and preparing the grid for the transition to a Net Zero carbon-free system by 2030. The company, whose sole shareholder is the Secretary of State for Energy Security and Net Zero, currently Ed Miliband, employs approximately 2,200 staff and costs the average household £6.46 annually through energy bills. Its 2024/25 annual report indicated a loss of £409 million, covered by taxpayers.
The complexity of balancing the grid is illustrated by Neso's own interactive game, which simulates the task of matching electricity supply with demand in real-time. The grid must maintain a frequency close to 50Hz, with an acceptable operating range of 0.4 percent either side. Deviations can damage equipment and trigger outages. The game highlights the challenge of managing renewable energy sources like wind and solar, which cannot be controlled at will and are dependent on weather conditions.
According to energy consultancy Watt-Logic, on June 23, the grid's frequency dropped dangerously low, indicating insufficient power supply. This occurred despite Neso issuing a "margin call" to electricity generators in anticipation of increased demand from air conditioning units during the heatwave, and potential issues with solar farm output due to high temperatures. Traditional power plants with spinning turbines act as buffers for the grid, but a high reliance on solar generation can reduce the availability of these buffers.
Transition to Renewables and Grid Challenges
Britain's electricity grid was originally designed around centralized coal-fired power stations, making it less suited for a system increasingly reliant on dispersed, weather-dependent renewables. Ed Miliband has previously adjusted the ambition for a carbon-free grid by 2030 to 95 percent. Initial cost estimates for grid upgrades to meet this target have risen significantly, from £58 billion to £89 billion. Experts and union leaders have raised concerns about the feasibility and cost of achieving a Net Zero electricity system by 2030, citing challenges in building the necessary infrastructure, such as offshore wind farms.
Neso's plans also include a requirement for "consumer-led flexibility," which could involve encouraging or mandating reductions in energy use during peak times, potentially through price surges. This raises concerns that consumers may ultimately bear the cost of the transition through higher prices or disruptions.
The government has confirmed that an independent inquiry into the events of June 23 is underway. Neso's Chief Executive, Fintan Slye, reportedly dismissed allegations of breached security standards and criticized whistleblowers for sharing their concerns.