LONDON — Britain’s energy regulator, Ofgem, has launched an official enforcement investigation into National Grid Electricity Transmission (NGET) as a direct result of the findings in the report on the North Hyde Substation fire, which occurred on March 20, 2025, which led to the shutdown of London Heathrow Airport (LHR) on March 21, 2025, disrupting over 1300 flights and affecting nearly 300,000 passengers.

According to the energy regulator, the incident was caused by a preventable technical fault, specifically a failure in a high-voltage transformer bushing at the North Hyde substation, which had not undergone any maintenance for eight years. Energy Minister Ed Miliband stated the situation as Heathrow shutdown: National Grid failures led to fire, says report  “deeply concerning” (Aslim,2025).

Scope of the investigation

During the Investigation, it was revealed that elevated moisture levels in the bushing insulating oil had been detected as early as July 2018. Still, no corrective action was taken by National Grid Electricity Transmission, the entity responsible for maintaining the substation. These moisture levels caused a short circuit, creating a spark that ignited the oil, resulting in a fire that quickly shut down the entire Heathrow airport and affected tens of thousands of other customers in west London.

This outrage led to incapacitated airport safety and security systems all over LHR, resulting in a total halt for over 12 hours. The final report highlighted that LHR had accepted the risk of such an unfortunate event as a “ High impact low probable “ Scenario, but the progressive effect revealed gaps in both energy and airport contingency planning.

Awareness of this incident has prompted urgent demands for improved maintenance procedures and stronger collaboration between sectors to enhance the resilience of the nation’s critical infrastructure, as well as to prepare for preventing future disruptions that affect critical safety infrastructure.

​​Key Actions

Ofgem will examine whether NGET complied with relevant legislation and licence conditions regarding the development and maintenance of its electricity system at North Hyde.

The regulator has commissioned an independent audit of NGET’s most critical assets to determine whether the identified failings were isolated or indicative of systemic issues across the National Grid estate. Ofgem will also work with the Civil Aviation Authority (CAA) and the Department for Energy Security and Net Zero to review lessons for the resilience of both the transport and energy systems.

The investigation could lead to fines, compliance orders, or even license revocation if breaches are confirmed.