Heathrow – the UK’s and Europe’s busiest airport – closed for hours until about 6pm on Friday while thousands of homes were left without power in the area. Counterterrorism detectives confirmed last week the matter is no longer ‘a potentially criminal matter’ after they were called in to investigate the fire.

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 official said he had raised concerns about Heathrow’s electricity supply days before a power outage forced it to shut down. Heathrow disputed the relevance of the official’s comments.