The National Grid’s chief executive has said Heathrow had “enough power” from other substations following Friday’s fire that caused the airport to shut down.

John Pettigrew told the Financial Times on Sunday the fire that knocked out a substation was a “unique event”, but that two other substations remained operational and capable of powering the airport in west London.

Heathrow’s chief executive had earlier said the shutdown it caused was not due to a lack of power, but was due to the time it took to switch from the damaged substation to the other two.

Asked whether she had full confidence in Heathrow’s management, Transport Secretary Heidi Alexander said it was a matter for the airport’s board.

Heathrow shut down operations for 18 hours on Friday, causing thousands of flights to be cancelled and leaving passengers stranded across the globe. The incident also disrupted the supply of millions of pounds of goods that go through the airport.

The fire started in a transformer within the electrical substation in Hayes, north of Heathrow, around midnight.

The airport has emergency back-up power supplies, which use diesel generators and batteries, but these only keep crucial safety systems running, such as landing equipment and runway lights.

A separate biomass power generator also provides heat and electricity to Terminal Two.

However, the National Grid is the main source of power for Heathrow.

Mr Pettigrew told the Financial Times he couldn’t remember a transformer failing to such an extent in his 30-year career in the industry.

“Losing a substation is a unique event but there were two others available. That is a level of resilience.”

He added: “There was no lack of capacity from the substations. Each substation individually can provide enough power to Heathrow.”

A Heathrow spokeswoman said that Mr Pettigrew’s comments “confirms that this was an unprecedented incident and that it would not have been possible for Heathrow to operate uninterrupted.

“Hundreds of critical systems across the airport were required to be safely powered down and then safely and systematically rebooted,” she said.

“Given Heathrow’s size and operational complexity, safely restarting operations after a disruption of this magnitude was a significant challenge.”

On Friday, Heathrow managers decided to close the airport on safety grounds while they switched to the alternative National Grid supplies.

Its chief executive, Thomas Woldbye, told the BBC the delay in reopening was due to the need to “reallocate” the power supply – “closing down and restarting systems which takes a long time”.

He said there were a “number of systems we have to shut down and then bring them back up and ensure they are safe”.

“It’s fuelling systems, its bridges, it’s escalators, all of these systems have to be brought back up, tested to ensure they are safe.”

He added that there were risks “of certain sizes we cannot guard ourselves against 100% and this is one of them”.

However the duration of the shutdown has infuriated airlines.

Willie Walsh, the former British Airways boss and head of the airline organisation IATA said it was a “clear planning failure by the airport” and the systems and procedures for handling power failures are now under the spotlight.

The government’s ordered a six-week investigation into the shutdown, led by the National Energy System Operator.

Mr Woldbye, who attracted criticism for claiming the airport had “come back quite fast”, said he was “happy” to answer to the prime minister.

Questioned on whether she remained confident in the decision making of Heathrow’s management on BBC Breakfast, Transport Secretary Heidi Alexander noted that the airport “is a private company”.

She added: “The individuals who need to ask themselves whether they have full confidence in Heathrow management are the Heathrow board.”

Simon Gallagher, managing director of UK Network Services, a consultancy specialising in power grids, said every airport in the UK had the same “vulnerability” to National Grid faults.

He said that a data centre near Heathrow entirely backs up its power sourcing, and that it was a “fair question to ask” why the airport had not been protected in the same way.

“It’s a hard argument to make to say that data centres are more important than Heathrow,” Mr Gallagher told BBC Radio 4’s Today programme.