Chaos at Heathrow Airport ensued after decades-old equipment caught fire - Kirsty Wigglesworth/AP

National Grid has skipped crucial maintenance on dozens of electrical substations across the UK, posing the risk of more disasters like the catastrophic fire that shut down Heathrow.

More than 100 high-voltage substations, which help move electricity around the country, are behind schedule for work, an official report has found. 108 of the Grid’s 805 substations are “outside” of their maintenance schedule, the National Energy System Operator (Neso) found.

The revelation comes from an official investigation into the fire in March at North Hyde substation, west London, which brought Heathrow to a stand-still and caused disruption for thousands of people.

Neso’s report said National Grid ignored dangerous faults at North Hyde, repeatedly deferred crucial maintenance and even left a broken fire suppression system in place for years. The issue that cause the fire was first identified in 2018.

News of maintenance delays elsewhere will raise concerns that similar disasters could occur in future. Recent months have seen an epidemic of puzzling fires and failures across Britain’s electricity network, as unexplained outbreaks have erupted from Exeter to Glasgow.

There have been five more blazes since the Heathrow fire, making a total of eight in about 10 weeks between the beginning of March and mid-May.

National Grid runs the high-voltage transmission system for England and Wales, with 5,500 miles of cables and 22,000 pylons giving it a monopoly that generated £5.4bn in operating profit last year. John Pettigrew, its chief executive, was paid more than £6m.

Substations are an essential part of the electricity system, containing transformers that step up voltages for efficient long-distance transmission and then step them down again for delivery to consumers and businesses.

Many of the UK’s substations are decades old, dating back to the 1960s or even the 1950s, meaning they need regular checks and maintenance.

Regulator steps in

Ofgem, which has opened an enforcement investigation, said: “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.”

A spokesman for National Grid said that following the Heathrow substation fire it had launched a programme to check maintenance records in case other substations were at risk of similar errors, carried out risk assessments for all operational sites and tested the resilience of substations serving critical infrastructure.

The spokesman said: “National Grid has a comprehensive asset inspection and maintenance programme in place. As described in the Neso report, our maintenance policy identifies intervals for asset maintenance and inspection.

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“Our policy recognises that for a number of reasons, including the need to secure planned system outages with Neso to safely deliver work, not all of our work may be carried out to exactly those intervals.

“Where that is the case, we will carry out a deferred maintenance risk assessment that defines the criteria to meet to allow the maintenance to be deferred, and what mitigations should be in place during the deferred period.”

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