Why Heathrow shut down: fire, reopening & investigation

21 March 2025

The airport reopened before the cause was fully explained

A fire at North Hyde disrupted Heathrow’s electricity supply and stopped normal operations. The original newspaper headline described the specialist police inquiry; that role was not a finding that the fire was a terrorist attack. ITV’s evening report said the blaze was believed to be non-suspicious and that some flights were resuming.

The first reopening changed the immediate task for stranded passengers and airlines. It did not explain the equipment failure, the earlier warning signs or why alternative supplies had not kept the whole airport running.

ITV News Meridian · reopening report · 21 March 2025 · Associated Press · reopening and backlog · March 2025

28 May 2025

Heathrow’s own review backed the response, with lessons to act on

The airport-commissioned Kelly Review concluded that Heathrow had made appropriate decisions during the incident. Heathrow’s published response committed its team to carrying out the recommendations.

That was an assessment of preparedness and handling, rather than the later technical explanation of the substation fault. The Business Continuity Institute’s analysis noted the review’s recommendations on critical-utility masterplans and the gap between technical knowledge and wider leadership awareness. Backing decisions on the day did not mean resilience improvements were unnecessary or already complete.

Heathrow · Kelly Review publication and response · 28 May 2025 · Business Continuity Institute · Kelly Review analysis · 29 May 2025

2 July 2025

The technical review found an earlier warning

NESO’s review identified a failed transformer bushing, most likely after moisture entered it. It said an elevated moisture reading had been recorded in 2018, but appropriate mitigating actions had not been implemented.

Reuters reported the findings and National Grid’s response that it had a comprehensive maintenance programme and had taken further action after the fire. The technical account identifies a failure and missed action; it is not a court judgment or the final outcome of the regulator’s enforcement case.

NESO · final technical review · 2 July 2025 · Reuters via London South East · findings and company response · 2 July 2025

2 July 2025

Three supplies did not mean an instant switch

The review also explained why the existence of three supply points did not prevent the shutdown. Losing one affected operationally critical systems; Heathrow’s internal network needed reconfiguration and safety checks before the other supplies could be used.

NESO records limited reopening late on 21 March and full operation from 22 March. That operational milestone did not mean every displaced passenger or aircraft was immediately back where it should be. AP’s reopening account described the continuing backlog.

NESO · final technical review · 2 July 2025 · Associated Press · reopening and backlog · March 2025

18 November 2025

The response extended beyond Heathrow

The government published a response to NESO’s recommendations, setting out an implementation plan for energy infrastructure, restoration and the resilience of critical services. It also committed to an Energy Resilience Strategy.

Those were policy commitments and planned actions. The existence of the response does not establish that every recommendation, new standard or cross-sector arrangement had been delivered. The closure had exposed dependencies reaching beyond one airport.

UK government · response and implementation plan · 18 November 2025

11 March 2026

A wider audit offered reassurance and work to do

Ofgem published the outcome of DNV’s audit of equipment and maintenance arrangements at 20 National Grid Electricity Transmission substations. The regulator welcomed its broadly positive assessment of asset-management practices while identifying five areas for review and improvement.

The requests covered maintenance standards and targets, deferred work, transformer-bushing tests and the new management platform. A wider audit can offer reassurance while still calling for changes. It did not close the separate North Hyde enforcement investigation.

Ofgem · wider substation audit · 11 March 2026 · Ofgem · improvement requests · 9 March 2026 · Ofgem · North Hyde enforcement case · current status

11 March 2026

The company supplied targets, not a completed checklist

NGET’s response gave April 2026 targets for several reviews and changes, with maintenance-target work extending to December. It described a new management platform as being tested and proposed quarterly updates. It also marked one guidance revision complete.

Those statements need to keep their original status: a target is not evidence of delivery, and a reported completed guidance revision does not complete every other action. The current Ofgem case page remains marked Open and says that opening an investigation does not establish non-compliance. The accountability question is still unresolved.

National Grid Electricity Transmission · response and targets · 11 March 2026 · Ofgem · North Hyde enforcement case · current status

The evidence

Sources for this update

Where the story stands

The airport reopened. The accountability work is still open.

Ofgem’s current case page remains Open. This account does not treat the wider audit as exoneration or company targets as completed work. An enforcement decision or documented implementation would change that position. Research checked 27 October 2026.

Stay updated

Heathrow’s power-cut shutdown: what caused it, and what changed?

The first inquiry was only the beginning

Flights resumed, and a technical review identified a preventable fault and missed maintenance action. A wider audit and improvement plan followed. Ofgem’s North Hyde case remains open; the technical findings are not a final regulatory judgment.

The story, in dates