National Grid says it’s restored power across Heathrow Airport, at least temporarily.
Anti-terror police are leading the investigation into a nearby substation fire.
A fire at an electrical substation in Hayes last night lead to a power outage which also affected 70,000 homes at its peak.
At least 13,00 flights are being diverted or cancelled and 200,000 passengers are stranded.
Travel Editor Simon Calder expects delays to last into the weekend.
