Heathrow airport was warned about its power supply in the days before the entire hub was shut down due to an outage that caused massive disruption, lawmakers were told on Wednesday.

Nigel Wicking, chief executive of Heathrow Airline Operators Committee, which represents airlines that use the airport, said he reported his concerns on two occasions.

“It was following a couple of incidents of, unfortunately, theft of wire and cable around some of the power supply that, on one of those occasions, took out the lights on the runway for a period of time,” he told a parliamentary committee on transport.

“That obviously made me concerned and, as such, I raised the point I wanted to understand better the overall resilience of the airport,” he added.

Wicking said he spoke to the Team Heathrow director on March 15 and the chief operating office and chief customer officer on March 19.

A fire late on March 20 at an electricity substation at Hayes in west London triggered the airport’s complete closure for most of the following day, affecting thousands of passengers around the world.

The closure of Europe’s busiest airport due to a single fire at a substation has raised concerns about its resilience.

The government has ordered a six-week investigation into the shutdown.

In the days after the closure the head of the UK’s national grid questioned the need to close the airport saying there had been “enough power” to keep it running.

“Losing a substation is a unique event — but there were two others available,” National Grid chief executive John Pettigrew said.

Heathrow chiefs, however, have insisted the closure was due to the time needed to switch to the other substations and make safety checks.