Review and investigation of energy system operation during extreme heat

Great Britain (England, Scotland and Wales) has one of the most reliable and resilient electricity systems in the world.

NESO is responsible for operating the system and during June’s record temperatures, they managed periods of high demand and lower generation with no disruption to customers’ electricity supplies. 

Balancing the electricity system is NESO’s core responsibility, and they have a range of tools available to them to manage it effectively, even under challenging conditions like June's heatwave. 

We remain very confident in Britain’s security of supply. At no point has there been any concern about meeting demand. The system has operated reliably throughout, as it is designed to do. 

However, Ofgem takes the recent allegations concerning the operation of the electricity system during the period of extreme heat in June, and the associated whistleblowing concerns, extremely seriously. We also consider it of first importance to examine and learn from any system incident to continually improve system security. 

It is important that these matters are examined thoroughly, objectively and transparently. Confidence in the operation of Great Britain’s electricity system depends not only on the resilience of the system itself, but also on confidence that serious concerns are investigated rigorously and independently.  

There are two distinct but complementary pieces of work underway, each serving a different purpose. 

Independent investigation into the whistleblowing allegations 

On Monday 13 July, NESO announced an independent investigation by law firm Eversheds Sutherland into the specific whistleblowing allegations that have been raised. The investigation will examine operational decision making and record-keeping. 

Ofgem has already committed to overseeing this investigation and we are setting out further details. An independent representative panel made up of Jayne Scott the Chair of the Audit and Risk Assurance Committee, Siobhan Duffy the Shareholder Non-Executive Director, and Akshay Kaul Ofgem Director-General, will be receiving all materials directly from Eversheds before any wider distribution. As NESO’s regulator, Ofgem is providing our oversight so that the investigation can examine the allegations objectively, independently and thoroughly.

This independent panel will ensure that all NESO staff who feel they have relevant information will be able to speak directly to Eversheds completely anonymously, and the investigation team will also be allowed to speak to whomever they wish, anonymously.  

NESO staff can also directly use Ofgem’s own whistleblowing process at www.ofgem.gov.uk/about-us/transparency/whistleblowing or email: whistle@ofgem.gov.uk 

Post-event regulatory review of the operation and management of the electricity system during the June heat event

Ofgem has also used its regulatory powers under Condition C7.5 of the ESO Licence to formally commission NESO to deliver post-event analysis and assessment of the incidents of system stress during extreme heat across the week of 22 June. This will cover the weather situation, system conditions and operational decisions, including compliance with all relevant security standards and lessons for the future. Specifically: 

1. establish the circumstances that led to the system event on the 23 June 2026 and the EMNs that were issued on the 24 and 26 of June
2. review the actions taken by the control room, system conditions and market actions including what decisions were made and why
3. review and identify if there were any breaches to any of the applicable rules and regulations, including but not limited to ESCQR, Grid Code, SQSS, FRCR and SOGL
4. the sufficiency of control room records to determine all of the above
5. identify any potential learnings from these events to ensure secure and stable system operation in the future 
6. share the findings with Ofgem, the Energy Secretary, other government bodies as applicable and ultimately publish

NESO will provide their analysis directly to Ofgem and independently of NESO's executive management. Where necessary, Ofgem may require further information, commission additional analysis, or conduct follow-up interviews with relevant operational personnel before reaching its conclusions. 

Ofgem will use the analysis and assessment provided to review the securing of the system during the June heatwave. Our purpose is to establish what happened, understand the operational context and decision-making, identify lessons for the future and determine whether any regulatory issues arise. We will take account of relevant findings from the independent legal investigation where those findings are material to understanding the management of the event or any regulatory implications but will not duplicate the independent investigation into the specific whistleblowing allegations. 

Transparency will be a central principle throughout and Ofgem’s goal is for all reviews to publicly provide full and comprehensive answers. NESO's post-event analysis, and Ofgem's conclusions, will be published, subject only to limited redactions required to protect the anonymity of individual staff members, commercially sensitive information, matters of national security, or other legitimate confidentiality considerations. 

Should either review identify issues warranting further regulatory scrutiny, Ofgem will consider what additional action is required and will utilise the full range of its regulatory powers where appropriate. 

Our focus throughout will be to establish the facts, follow the evidence wherever it leads and act independently in the public interest. It is essential that the circumstances surrounding this event are fully understood, that any necessary action is taken, and that lessons are identified to strengthen the resilience, safety and effective operation of Great Britain's electricity system. We are committed to completing this work rigorously, transparently and at pace, while ensuring confidence in the integrity of both the process and its outcomes. 

Full technical Terms of Reference will be published in due course.  

Ofgem Formal Post Event Review request

To: National Energy System Operators Limited  

Request under Condition C7.5 (Energy resilience and resilience reporting) of the Electricity System Operator Licence to provide post-event analysis and assessment 

1. The company to which this request is addressed (“NESO”) is the holder of an Electricity System Operator Licence (“ESO Licence”) treated as granted under Section 6(1)(da) of the Electricity Act 1989 and a Gas System Planner Licence (“GSP Licence”) granted under Section 7AA of the Gas Act 1986.  
    
2. The Gas and Electricity Markets Authority (“the Authority”)¹ issues this request, under Condition C7.5 of the ESO Licence. 
    
3. In late June, during a period of extreme weather, Great Britain’s power system experienced operability challenges and tight margins. This resulted in NESO issuing Electricity Margin Notices for the evening peak periods on 24 June and 26 June. 
    
4. The Authority, pursuant to Condition C.7.5, hereby requests NESO to conduct a comprehensive review into all periods of significant system operation challenges during the week of 22 June. NESO must explore the drivers of system stresses, the actions taken by NESO and the market including decision making and record keeping, the precise security status of the system against relevant security standards, and any wider system operation lessons to be learned, both now and in the future. 
    
5. The Authority, separate to this request, will work with NESO and DESNZ to set out and confirm the relevant actions to be completed for NESO to fulfil this request. 

Eleanor Warburton 
Director for Energy Systems Design & Development  
Duly authorised on behalf of the Gas and Electricity Markets Authority  
17 July 2026