Heathrow airport’s chief executive has said he was not aware of any airport “that has a backup supply that can switch on in minutes to the magnitude of what we experienced yesterday.”

“The same would happen in other airports,” Thomas Woldbye added.

Experts told The Telegraph, however, that some of Heathrow airport’s rivals have two or more external power feeds, and as many as seven times the number of backup generators.

Mr Woldbye defended the airport’s response after an electricity substation fire knocked out power at the London airport as well as its main back-up generator, closing it for most of Friday before some flights began to arrive and take off later in the evening.

The airport said it was fully operational on Saturday, but delays continued.

The shutdown has raised serious questions about the reliability of one of the UK’s most critical pieces of infrastructure, and has led to accusations that Heathrow’s power back-up falls significantly short when compared with other airports that see similar levels of traffic.