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.

The fire at an electrical substation was caused by a short circuit in a part that hadn’t been properly maintained by National Grid, an official report found.

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.