Is one blundering engineer responsible for crippling Heathrow? Airport bosses face questions over farcical shutdown that left 300,000 travellers stranded – as new theory emerges

Heathrow bosses were facing questions last night about how a small fire shut down one of the world’s biggest airports.

Tens of thousands of travellers are still stranded across the globe today after a blaze at an electricity substation cut power to the airport.

It resulted in unprecedented scenes, grounding flights for most of the day and exposing a major vulnerability in the country’s infrastructure.

Last night, a probe into the disaster was being led by counter-terrorism police, while Westminster sources blamed human error.

Nearly 300,000 passengers were affected by the meltdown, which led to the cancellation or delay of more than 1,350 flights. 

Some 120 transatlantic services were forced to turn round in mid-journey.

Passengers on flights from Singapore and Perth were diverted to Paris before taking buses to London.

As eight long-haul British Airways flights finally took off last night, analysts criticised the airport, the busiest in Europe, for its inability to rely on backup…