Policy paper

NESO review into the North Hyde Substation outage: terms of reference

Published 28 March 2025

Applies to England, Scotland and Wales

Introduction

Late evening on Thursday 20 March 2025, a large fire broke out at North Hyde Electricity Substation in Hayes, London. This resulted in over 60,000 customers and businesses losing power and significant secondary impacts to the aviation sector due to the associated closure of Heathrow Airport. Power was quickly restored to impacted customers, and Heathrow restarted operations from late 21 March. However, there was significant disruption at Heathrow Airport over the weekend of 22 and 23 March.

The Energy Secretary and Ofgem have therefore commissioned the independent National Energy System Operator (NESO), under condition C7.5 of the Electricity System Operator Licence, to review the incident, to identify lessons and recommendations for the prevention, and management of future power disruption events, and lessons for Great Britain’s energy resilience more broadly.

Scope

NESO will identify lessons and good practice, regarding energy sector resilience, including both Distribution Network Operators, and Transmission System Operators, and, where relevant, those essential services and sites with a critical dependence on continued electricity supply, using an evidence based approach. This review will not investigate the knock-on impacts to the transport sector as a result of the closure of Heathrow Airport, which will be covered in the Ruth Kelly review.

In particular, NESO will report on the following 3 pillars, in relation to this incident:

1. 1. Resilience of energy infrastructure:
   1. a. Report on the root cause, other contributing factors and sequence of events, of the outage at North Hyde electricity substation and subsequent supply disruption in the surrounding area (alongside the London Fire Brigade investigation).
   2. b. Assess direct and secondary impacts of the event across GB electricity networks, electricity customers, and critical national infrastructure, including why it resulted in the closure of Heathrow;
   3. c. Identify areas of good practice and where improvements are required for continued energy system resilience, considering relevant aspects such as asset management (including on or off-site mitigations), networks supporting the operation of critical national infrastructure (including internal networks that connect to the transmission or distribution systems) and future development of the electricity system;
2. 2. Response and restoration of energy infrastructure:
   1. a. Consider what contingency planning had been undertaken in relation to the failure of electricity infrastructure, and assess whether the plans were enacted as planned and delivered as expected during the incident; and
   2. b. Timeliness and effectiveness of the response to the incident, including communications with relevant stakeholders and the public.
3. 3. Enhancing the resilience of critical infrastructure to energy disruption:
   1. a. Make recommendations for improving the resilience of essential services, including critical national infrastructure, to power disruption.

The review will focus on the resilience of Great Britain’s energy system, given NESO’s remit to provide independent advice on the security and resilience of the whole energy system. However, key findings and lessons will be shared with Northern Ireland as appropriate to ensure UK wide resilience to energy risks.

For certain aspects of the review, NESO may rely on information and evidence gathered from other sources; for example London Fire Brigade, who continue to investigate the cause of the fire working close with electricity networks or other internal reviews currently being undertaken with regards to the outages. London Fire Brigade investigation will also explore the compliance of fire safety measures under the ‘Regulatory Reform (Fire Safety) Order 2005’ and any potential gaps in guidance or regulation.

During the review, NESO will draw on the expertise of the companies involved in managing and operating impacted electricity systems, operators of affected critical national infrastructure, regulators, government and others. The review will not look more widely into airport operations and the impact on customers of the airport and aviation industry.

Deliverables

NESO will submit an initial report to the Secretary of State and Ofgem within 6 weeks, with an initial assessment of the data available at this stage of the review.

NESO will provide a final report to the Secretary of State and Ofgem by end of June 2025, which will include recommendations and lessons for the future and where possible, a proposed implementation plan.

Key findings and recommendations of the review will be published by NESO.