National Energy System Operator publishes interim findings from the review into the North Hyde Substation outage

• Today, National Energy System Operator (NESO) publishes its interim findings from the review into the North Hyde Substation outage.
• This follows the Department for Energy Security and Net Zero (DESNZ) and Ofgem commissioning NESO to conduct a review, producing interim findings within six weeks and a final report by the end of June 2025.
• NESO’s interim report focuses on establishing the timeline and sequence of events of the outage, and outlines the further investigation required to deliver our final report in June 2025.
• The root cause of the fire that caused the outage remains unknown, with London Fire Brigade and National Grid Electricity Transmission continuing to conduct forensic investigations. The Metropolitan Police Service confirmed on 25 March 2025 that it had “found no evidence to suggest that the incident was suspicious in nature”.
• NESO anticipates that the final report will make findings and recommendations relating to the resilience of energy infrastructure; the response and restoration of energy infrastructure; and the resilience of critical national infrastructure to energy disruption.
• The report is based on an initial examination of the available evidence provided by key stakeholders. All evidence and information is subject to further review in advance of the final report.

Today (8 May 2025) National Energy System Operator (NESO) publishes its interim findings from the review into the North Hyde Substation outage which took place on 20 March and led to the closure of Heathrow Airport.

NESO was commissioned by the Department for Energy Security and Net Zero (DESNZ) and Ofgem to conduct a review into the outage, with an initial report submitted to the Secretary of State and Ofgem within six weeks. NESO will provide a final report to the Secretary of State and Ofgem by the end of June 2025, including recommendations and lessons for the future.

The interim findings published today are an initial assessment of the evidence we have gathered so far. This includes establishing a timeline and sequence of events of the outage, explaining the roles and responsibilities of the key stakeholders involved, and outlines further investigation required to deliver the final report by the end of June 2025. Information contained within the interim report may be refined or subject to change as the review progresses and further evidence comes to light.

NESO has several ongoing lines of enquiry which include:

• the result of London Fire Brigade’s and National Grid Electricity Transmission’s forensic investigations into the root cause of the fire and its spread;
• design standards for substation sites;
• maintenance history for assets at North Hyde;
• risk management and mitigation, as well as resilience planning;
• Heathrow Airport’s private network configuration, including its resilience;
• incident management coordination by key organisations;
• the response of other impacted organisations including Network Rail, Transport for London and the commercial customers of Scottish and Southern Electricity Networks.
   

NESO expects to publish its final report by the end of June 2025 and anticipates that this will make findings and recommendations in relation to the resilience of energy infrastructure, the response and restoration of energy infrastructure, including Heathrow Airport, and the resilience of critical national infrastructure to energy disruption, including working to a shared definition and understanding of resilience between sectors.  

Fintan Slye, Chief Executive Officer, National Energy System Operator said:

“I am very pleased to publish our interim findings from the review into the North Hyde Substation outage.

The outage led to the loss of supply to around 67,000 customers, a number of commercial customers and Heathrow Airport. It is important that the right lessons are learnt from this incident to prevent future instances where possible and to manage them effectively when they do occur.

NESO’s unique position in the energy sector makes it well placed to provide recommendations to improve the resilience of the country’s energy system, and the resilience of its critical national infrastructure.

I want to thank the organisations who have provided evidence to the review for their cooperation. We will continue to work with the key stakeholders as we move towards publishing the final report.”

View the full review