THOUSANDS of disgruntled travellers were plunged into darkness after a “catastrophic” power failure of the back up supply at Scotland’s busiest airport.

Edinburgh airport lost power at around 9am on Wednesday morning, causing lengthy delays to check-ins and flights.

Arrival and departures information showed hundreds of flights had been affected to destinations included Heathrow, Brussels, Malaga, Berlin and New York.

The airport —which is the six busiest in the UK — handles more than 12 million passengers a year.

A spokesman said that the airport had lost power due to a power outage on its high voltage supply, which knocked out the main supply to the terminal.

He said: “The fault also prevented our back up system from operating. This was caused by a catastrophic failure in one of our transformers.

“We are currently working to understand the full cause of the issue and why the redundancy didn’t function as designed.”

Passengers took to Twitter to post images of holidaymakers standing in the near dark as staff announced: “Please bear with us, a huge area has been affected by a power cut.”

Social media users also shared images which showed long queues leading to, and inside, the terminal building.

Planes were able to take off and land, however there were reports that around 30 flights were forced to sit on the runway while the security gates were down.

One user said: “Folks now getting agitated. No communication, no explanation. Not everyone on internet. No staff walking around explaining and reassuring.”

Another said he was stuck in Switzerland on a return flight, saying “Off to Edinburgh, but stuck at Zurich airport because of total power outtage at Edinburgh airport”.

One person tweeted: “Stuck in chaos. What modem airport doesn’t have emergency back up power. Total fiasco.”

Lothian Buses also said its services were unable to make their way into the airport due to the blackout.

A spokesman from the airport confirmed power was returned to the terminal around 10am though expected delays as it cleared the backlog.

Later, airport staff confirmed on social media at around 5pm that flights were beginning to return to their normal scheduled time.

One the airport’s Twitter account, staff said that flights on Thursday would not be affected, saying: “The power is all back and running, flights have resumed and service is returning as normal.”

Just last week, a survey revealed that the airport faced delays in nearly one in three flights, contributing to a surge in compensation claims. Already, around 27 per cent of more than 110,000 flights at Edinburgh Airport this year have been delayed by at least 15 minutes, an increase from 20.1 per cent two years ago.

Consumer watchdog Which? said at the time that holidaymakers are most likely to face delays when using Edinburgh Airport.