The National Energy System Operator (NESO) has confirmed in its interim report that the cause of the North Hyde Substation fire, which led to a major power outage and the temporary closure of Heathrow Airport on 21 March, remains undetermined.
The review, commissioned by the Department for Energy Security and Net Zero (DESNZ) and Ofgem, is being conducted in two phases, with the final report due at the end of June 2025. The interim findings present a timeline of the outage, detail the roles of the organisations involved in the response, and identify areas requiring further investigation.
Forensic investigations into the source and spread of the fire are ongoing, led by the London Fire Brigade and National Grid Electricity Transmission. On 25 March, the Metropolitan Police Service stated that it had “found no evidence to suggest that the incident was suspicious in nature”.
The interim report highlights several lines of enquiry still under review, including substation design standards, asset maintenance history, and risk mitigation measures. NESO is also examining Heathrow Airport’s private energy network configuration and the coordination of emergency responses by organisations including Network Rail, Transport for London, and Scottish and Southern Electricity Networks.
NESO Chief Executive Fintan Slye 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.
The final report is expected to include findings and recommendations relating to infrastructure resilience, energy system restoration, and cross-sector coordination in the event of future disruptions.
Heathrow’s response to the outage has also been questioned in Parliament, under investigation from the Transport Committee.
