HEATHROW and National Grid bosses face serious questions over how a single fire led to the closure of the airport and left tens of thousands of homes without power, Downing Street said today.

More than 200,000 passengers had their flights to or from Britain’s biggest airport cancelled or diverted after a transformer within the west London electrical substation caught fire.

“There are questions to answer,” a No 10 spokesman said. “We expect those questions to be answered but our clarity right now is on this incident being appropriately dealt with.”

A National Grid spokesperson said: “We’re sorry for the disruption caused by a fire at our North Hyde substation and for the loss of power supplies in the area.

“Working in partnership with the local network operator SSEN Distribution, the network has been reconfigured to restore all customers impacted, including the ability to resupply the parts of Heathrow airport that are connected to North Hyde.

“This is an interim solution while we carry out further work at North Hyde to return the substation and our network to normal operation.”

Prospect union said its Air Traffic Control and energy sector members were managing “significant extra work” round the clock.