The substation fire that closed Heathrow for almost a day in March cost the airport “tens of millions” of pounds, its chief executive has said.

Giving the hub’s first public estimate on the bill from the blaze, Thomas Woldbye said Heathrow had yet to decide whether to pursue National Grid for damages, as it awaited the findings of the energy regulator Ofgem into the incident.

Heathrow was criticised for its lack of resilience after more than 270,000 passenger journeys were disrupted when an overnight fire and power outage stopped flights landing or taking off on 21 March.

Woldbye, who slept through the night with his phone on silent, said he “would have liked to see my personal role play out differently”.

A report by the National Energy System Operator found that the fire was due to a known, preventable fault at the North Hyde substation, and insufficient action had been taken to remedy problems detected in 2018. Ofgem has launched an investigation.

Woldbye said that Heathrow would also be “investing in agreement with the airlines to improve the physical resilience” of the airport.

The comments came as Heathrow revealed that profits fell by a third in the first half of the year despite passenger numbers reaching a record high, with 39.9m journeys in the six months to 30 June.

Woldbye said the fall in pre-tax profits to £203m was down to higher costs, “primarily finance costs, as the consequence of higher interest rates”.

Heathrow this month submitted a five-year investment plan to the Civil Aviation Authority to improve its facilities and raise charges by about £5 a passenger. The airport is due to submit further plans next week to the government for a third runway, after the chancellor, Rachel Reeves, signalled support to restart the controversial scheme.

Woldbye said: “If we are to meet customers’ requirements, and I think we should, particularly on capacity, that will cost money. Heathrow is a very space-constrained airport. We already have two or three times as many passengers per square metre of airport as our competitors in Europe. Creating additional capacity is not easy, and hence it’s costly.”

He said the runway would not be in operation until 2035 at the earliest and indicated that the airport would be pursuing it with caution. “The government has asked for input. If customers are not clear, they want it, if the country is not clear they want it, why would we do this?”

The submission is expected to spell out the need for action on new flight paths and planning reform before Heathrow commits major investment, but it will include a “baseline plan” for the runway, which in its last iteration required major work and diversions to the UK’’s busiest motorway, the M25, and would increase the number of flights at Heathrow by up to 50%.

However, he added: “I think it is very important for the country, because I think we are already lagging behind on aviation capacity in the London area, and we’ll continue to do that for a while. We need to create the right conditions for both airlines and airport to make sure that it’s a success. Will Heathrow survive without a third runway? Yes.”