Heathrow Airport was warned about the "resilience" of its power supply in the days before a fire which shut down the airport for more than a day last month.

The boss of a group representing airlines told a group of MPs on Wednesday that he spoke to Heathrow on 15 March about his concerns and again on 19 March.

Heathrow Airline Operators' Committee boss Nigel Wicking said he raised cases of "theft of wire and cable around some of the power supply" which he said temporarily took out runway lights, which are critical to passenger safety,

Heathrow boss Thomas Woldbye apologised to the nearly 300,000 passengers whose journeys were disrupted by the closure on 21 March.

He offered his "deepest regrets" adding that the "situation was unprecedented". The airport was shutdown after a fire at an electrical substation.

Speaking to MPs on the transport committee, Mr Wicking said the temporary failure of the runway lights which he noticed before the fire "obviously made me concerned, and as such I'd raised the point".

"I wanted to understand better the overall resilience of the airport."

He added: "It is the most expensive airport in the world, with regard passenger charges, so from our perspective, that means we should actually have the best service, we should have the best infrastructure."

He said he had spoken to the Team Heathrow director on 15 March about his concerns - six days before the fire - and the chief operating officer and chief customer officer on 19 March.

On the day of the shutdown, airlines had to divert 120 aircraft, which is "not a light decision to be made in any context", he added.

As a consequence, when Mr Wicking joined a call with NATs, the national air traffic service, at 05:30, "they'd run out of space within the UK for aircraft to divert".

"Aircraft were then going to Europe, and then some were even halfway across Europe and going back to base in India," he said. "So, quite a level of disruption for those passengers, let alone all of the cancellations".

'Losing power'

Mr Woldbye said Heathrow realised "during the early hours" of Friday 21 March that "we were losing power to the airport".

"In our operations centre you would seen all the red lights go, that the systems were powering down," he said. "We had no information as to why."

"We then had a slightly later stage call from the fire department that the substation was on fire," he said.

Heathrow is supplied by three substations, but knocking out one caused the airport to shut down.

Mr Woldbye said a third of the airport was powering down and that Terminal 2 was particularly affected, along with certain central systems. He added that it became "first and foremost a safety situation".

"We need to make sure, when a crisis happens, that people are safe," he said.

The first priority was to check that no-one been caught in lifts or was hurt.

Safety critical systems such as runway, runway lighting and the control tower "switched in as they should", however, he said.

When asked why the airport had not reopened sooner, Mr Woldbye said that could have meant passengers got hurt.

He said: "If we had got this wrong, we might be sitting here today having a very different discussion about why people got injured, and I think it would have been a much more serious discussion.

"So there is a margin within which our people have to take very serious safety decisions, and that is what they are trained for, that is what they do, and that requires that every single system is up and running, tested and safe."

However, Mr Wicking said Terminal 5 could have reopened sooner.

He said: "In terms of T5, my understanding both from British Airways but also on the day, was that pretty much everything was fine to operate by mid-morning, by 10 o'clock."