The national grid operator has come under scrutiny following reports that it may have withheld critical public warnings about a near-blackout event during a heatwave in June, raising concerns of a possible cover-up. Two separate investigations into the state-owned National Energy System Operator (Neso) revealed that the organisation did not issue alerts about potential electricity rationing despite internal guidelines recommending such disclosures.

The issue emerged after engineers observed that power network frequency—a key indicator of grid stability—fell below normal limits for an extended period amid hot weather. According to eyewitness accounts from the control room, warnings about the need to reduce electricity demand “should now have gone out” on June 23, though not all witnesses agreed.

Shadow energy secretary Andrew Bowie expressed serious concerns following the release of the investigation findings. He accused both the grid operator and regulators, including Ofgem, of protecting individuals within Neso while significant gaps and unexplained decisions in the reports remained unaddressed. Bowie highlighted missing information and incomplete records, especially relating to a decision made on June 23 about spare electricity reserves for the following day.

Typically, engineers plan to have enough electricity to meet expected demand plus a safety margin to mitigate unexpected issues. If forecasts indicate a shortfall significant enough, Neso’s guidelines require warnings to be issued to network operators. These warnings prompt demand-reduction measures such as lowering voltage or disconnecting users temporarily. However, internal documents showed that certain reserve requirements—500 megawatts for the heatwave and an additional 100 megawatts linked to changes in reserve services—were removed from shortage assessments rather than reinforced.

An internal note suggested that part of the reserve was excluded because including it would have triggered a warning about electricity rationing, a move which could have been "embarrassing," according to independent consultant Andrew Larkins. Larkins emphasised the importance of timely warnings, noting that late alerts reduce the time for the electricity industry to prepare, potentially threatening grid stability.

While investigators questioned whether adjustments to reserve calculations were intended to downplay the severity of the situation, Neso maintained this was not the case and deferred technical judgment to a separate review. Neso added that crossing numerical thresholds did not mandate automatic warnings, emphasizing that engineers must consider overall conditions before deciding on appropriate actions.

Whistleblowers had earlier alleged that corporate affairs personnel interfered with engineering operations during the incident, but the law firm Eversheds Sutherland, which conducted one of the inquiries, found no evidence to substantiate these claims. However, the firm did identify a “culture of reputational sensitivity affecting operational decision-making” within Neso.

Neso stated that the independent investigation found no proof supporting any specific allegations against the organisation. Ofgem confirmed it will review all relevant evidence from the Eversheds report as part of its ongoing assessment.

Eversheds Sutherland declined to comment on the matter. The controversy raises questions about transparency and the adequacy of the national grid’s response during periods of extreme demand.