Q: What happens when a suitcase is left in an airport toilet? A: Total chaos

The bag, later found to be empty, was discovered in a public toilet at Edinburgh Airport's main terminal, sparking a full-scale evacuation of the building and lengthy delays.

A police inquiry was under way last night to try to trace the owner of the large case, which was discovered in the ladies' toilets of the domestic arrivals area by a member of staff at a Costa Coffee bar at about 2:20pm. It was destroyed by military bomb disposal experts.

Officials at the airport – which was expecting to handle about 35,000 passengers yesterday – said the find came at the "worst possible time", because it coincided with the first day of the school holidays in the city.

Three incoming flights from London were cancelled and about 150 others were delayed for up to three hours, while the army's bomb squad carried out its investigation, before giving the all-clear at about 5pm.

Passengers were told to leave the arrivals hall, main check-in area at the terminal building, the food courts and shops, and gather at safety areas outside.

The scare led to major traffic disruption around the airport, with tailbacks stretching back about a mile. Some passengers faced lengthy walks to the airport after being dropped off by shuttle bus from the city centre.

A spokesman for airport operator BAA said there were "significant knock-on delays for passengers".

He added: "This kind of incident is pretty unusual, but has happened before.

"There is a security concern over any unattended luggage and we have established procedures that are put in place when a bag cannot be accounted for.

"However, it was the worst possible day, because the school holidays have just started and the airport was very busy."

As the area is open to the public, the bag would not necessarily have been checked in.

One insider said: "It's a bit of a mystery as to how this bag got there. It's pretty normal for luggage to be left abandoned, but not an empty bag. Obviously, it's a bit strange and that's why there are efforts ongoing to track down the owner."

A police spokeswoman said:

"As a result of this discovery, the terminal building was evacuated, and the army EOD (explosive ordnance disposal] team were called to attend. They examined the luggage, and found that it posed no threat.

"Inquires are under way to establish how the luggage came to be located within the toilets."

Earlier, Edinburgh police were forced to evacuate all staff from their headquarters at Fettes Avenue to a nearby high school after mailroom staff raised the alarm over a suspect package.

Police last night said there was nothing to connect the two incidents. More than 350 police staff faced a three-hour wait to return to the building while the bomb squad inspected the package, later described as a hoax by senior officers.