Heathrow Airport is considering legal action against National Grid after a report found the fire which caused the airport to shut down was a result of a known fault at an electrical substation.
An investigation found that National Grid, which owns the substation which supplies Heathrow, had been aware of a problem since 2018 but failed to fix it.
There were numerous opportunities to rectify moisture affecting electrical parts at the North Hyde substation, but maintenance was repeatedly deferred, the report said.
Heathrow told the BBC National Grid "could and should" have prevented the fire and that it expected it to "take accountability for those failings".
"Those failings that resulted in significant damage and loss for Heathrow and our airlines," a spokesperson added.
National Grid said it had taken action since the fire on 20 March, but said such events were "rare" and that Britain had "one of the most reliable networks in the world". It has not yet responded to Heathrow's potential legal case.
Following the report being released on Wednesday, energy watchdog Ofgem has launched its own investigation into National Grid.
Heathrow, the UK's biggest airport, shut down as a result of the power cut, which led to thousands of cancelled flights and stranded passengers.
The National Energy System Operator (Neso) said moisture entering electrical components at the substation caused the blaze.
It said "elevated" moisture had been detected in July 2018 and that under National Grid's guidance, such readings indicate "an imminent fault and that the bushing should be replaced".
Bushing is insulating material used around electrical parts.
But it said the issue went "unaddressed" and "basic maintenance" to fix the problem in 2022 was deferred.
More than 270,000 journeys were affected by Heathrow's shut down and the impact was also felt beyond the airport, with "essential services" including road, rail and Hillingdon Hospital affected, Neso said.
Airlines based at Heathrow have said the closure on 21 March cost carriers between £80m to £100m.
The power failure and subsequent closure of the UK's busiest airport has raised wider questions about the UK's major infrastructure resilience.
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