An inquiry has found that an electrical substation fire that shut down Heathrow Airport in March was caused by a preventable technical fault identified almost seven years earlier

A fire that shut Heathrow airport in March, stranding thousands of passengers, was caused by National Grid's failure to maintain an electricity substation, an official report said on Wednesday, prompting the energy watchdog to open a probe.

National Grid has insisted its management teams were “not made aware” of problems at a London electricity substation years before a fire in March that led to the closure of Heathrow airport for 24 hours.