The New Look store was demolished after the April 2007 fire
High Street fashion chain New Look has been fined a record £400,000 for fire safety breaches after a blaze broke out at a central London branch.
Staff initially ignored smoke pouring out of a window at New Look in Oxford Street, Southwark Crown Court heard.
A fire alarm sounded but was switched off until staff finally "panicked" and evacuated customers. No-one was hurt.
Judge Geoffrey Rivlin QC said the April 2007 fire could have been "a disaster almost too awful to contemplate".
The court heard that the store was filled with early evening shoppers on 26 April 2007 when the fire began in its second floor storeroom.
Shopper Joanne Weaver said the fire alarm went off "intermittently" but an initial absence of staff reaction did nothing to "suggest there was a problem".
She wandered down to the basement and browsed through the shop's shoe section with 20 other customers until a staff member told her the place was being evacuated.
Ms Weaver said she ran up an escalator, across the ground floor and out through the front door.
"I could hear the sound of windows breaking - and I felt the heat," she said.
"Staff within the shop did not seem to have a plan to evacuate people. They went from no cause for alarm, to panic."
Some customers fell over as they fled the store while others ducked shards of glass falling from above, the court heard. The store's windows were blown out in the fire.
The court heard that all 150 people in the store escaped unharmed and another 300 were evacuated from neighbouring premises.
The cause of the fire was never discovered. It "virtually gutted" the building, which subsequently had to be demolished.
'Potential for tragedy'
New Look was fined £250,000 for failing to supply a "suitable and sufficient" fire risk assessment for the premises and £150,000 for failing to adequately train staff.
It was also ordered to pay more than £136,000 costs.
The fines represent the largest imposed since new fire safety legislation came into being in 2006.
The judge said the charges represented "significant failures" which "constituted a risk of death and serious injury".
"We are here dealing with a multitude of very real and deeply disturbing breaches, resulting in a system falling a very long way below the standard required and to be expected of a company of this size," he said.
"As a result of these failures the potential for real human tragedy was always there."
Outside court, a New Look spokesman said: "The incident in 2007 was an unfortunate and concerning time for us all, and as a responsible business we immediately initiated a comprehensive review of our health and safety procedures."
He said the firm had "fully taken on board the recommendations presented at the inquiry" and "will continue to strengthen its company guidelines and working practices to ensure full compliance".