Firefighters were called to the scene in the early hours of Monday morning after customers had been seen choking and spluttering in one area of the club. Crowds were evacuated by the time the crews arrived at 1.30am.

Clubbers described scenes of panic as hundreds of people tried to flee Lulu.

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One witness said the lights went on and the bouncers started shouting to get out in a scene of “complete chaos”. She said: “The lights went on and the bouncers started shouting for everyone to get out and for us to cover our faces. It was a terrifying stampede – you could not move.”

She said that the fear and rising panic meant people were pushing each other from every direction.

“Lots of people were coughing, and I have cuts on my feet as lots of glasses were smashing. There was a body against your front, someone at your back and people pushing from either side. My main concern if anything was to actually go wrong in there, there’s only one way out.”

Crowds were told to abandon their personal belongings and exit through the front door onto George Street.

Fire engines, equipped to deal with hazardous materials, were sent to the scene and following atmospheric tests taken shortly after the evacuation, the Scottish Fire and Rescue Service found no harmful substances present.

A body spray canister was removed for further analysis and determined by the authorities to be the most likely cause of the alarm.

“I don’t even know how everyone got out there without someone getting hurt, it was an absolute riot.” added a witness.

Another clubber said: “They need to take a look at their fire safety. How people never got hurt getting out I will never know.”

Duty manger Ethan Mack, who escalated the evacuation drill, had noticed a number of customers coughing and choking, also affecting the DJs who were playing, and realised something was amiss.

The venue’s owners have praised the quick response of the club’s staff.

David Johnston, development director at Montpeliers Group which owns Lulu, said: “I can’t praise the team enough for the action they took. They are trained for all sorts of eventualities, from deliberate pranks right up to terrorist attacks. That’s an unfortunate reality of the times we live in, so while this turned out to be nowhere near as serious as that, it is reassuring to know that all of the training we carry out is genuinely effective.

“I’d like to say a huge thank you to our customers, who helped us make sure the building was evacuated as quickly and safely as possible. He added: “Ethan’s response was 100 percent the right thing to do and the entire team deserve to be commended for the speed and efficiency of their actions. All of the bar staff and security staff played their part.