Ofgem has launched an official investigation into National Grid Electricity Transmission (NGET) following the catastrophic fire at the North Hyde substation in March that cut power to nearly 67,000 customers, including Heathrow Airport and triggered widespread disruption across London.
The regulator confirmed the probe, after NESO’s final report found the root cause was a preventable technical failure—specifically, moisture ingress into a transformer bushing.
“We have opened an investigation into National Grid Electricity Transmission,” said Akshay Kaul, Director General for Infrastructure at Ofgem.
“We have also commissioned an independent audit of their most critical assets. We expect energy companies to properly maintain their equipment and networks to prevent events like this happening. Where there is evidence that they have not, we will take action and hold companies fully to account.”
The watchdog will now assess whether NGET breached licence conditions or failed in its duty to maintain its infrastructure.
In parallel, it will launch an independent audit of NGET’s critical assets, to determine whether the fault at North Hyde was a one-off or a sign of deeper systemic risk across the Grid.
The fire on 20 March resulted in a full power loss from the 275kV substation, with knock-on effects across transport, healthcare and three data centres.
Thousands of homes and businesses were affected and local residents had to be evacuated.
Ofgem will also work with the Civil Aviation Authority and the Department for Energy Security and Net Zero to follow through on broader resilience recommendations in NESO’s review.
“Britain has one of most reliable energy systems in the world,” Kaul said. “We must continue to invest in the system to maintain that resilience.”
The regulator stressed that lessons must be learned fast, and all parties must act to ensure power infrastructure can withstand increasing demand and climate risks.
