Heathrow Airport Shutdown Linked to Seven-Year-Old Issue

After announcing its investigation into National Grid, Akshay Kaul, director general for infrastructure at Ofgem, said it expected energy companies to properly maintain their equipment and networks to prevent events like this happening.

\"Where there is evidence that they have not, we will take action and hold companies fully to account,\" he added.

National Grid said it had a comprehensive asset inspection and maintenance programme in place and that it had taken further action since the fire. It said this included re-testing the resilience of substations that serve strategic infrastructure and added it would cooperate with Ofgem's investigation.

Mr Slye said as well as the substation fault, there was also a potential missed opportunity at Heathrow to maximise its energy resilience and also another to across the energy industry around understanding resilience of critical infrastructure.

The report also said that it was not known to the energy companies that the loss of one of the electrical supply points - of which Heathrow has three - would result in a power outage to some of the airport's critical systems.

\"The review also found that energy network operators are not generally aware whether customers connected to their networks are Critical National Infrastructure,\" it said.

Heathrow Airport welcomed the report and said it expected National Grid to be carefully considering what steps they can take to ensure this isn't repeated.

\"A combination of outdated regulation, inadequate safety mechanisms, and National Grid's failure to maintain its infrastructure led to this catastrophic power outage,\" the airport said.

Nigel Wicking, chief executive of Heathrow Airline Operators' Committee, told the BBC that Heathrow's closure cost airlines between £80m-£100m.