The distressed worker - who had to be treated for hypothermia - was discovered after two-and-a-half hours by a colleague at the chain's Victoria coach station outlet on 29 July 2021.

Wearing just jeans and a T-shirt, she tried to stay warm by moving around, but her condition began to deteriorate.

Her breathing became increasingly difficult, and sensations in her thighs and feet started to fade.

In an attempt to shield herself from the cold air blowing from the ventilator, she struggled to tear up a cardboard box filled with chocolate croissants, but her hands were too cold to break it apart.

Following her rescue, an inquiry uncovered the absence of a suitable risk assessment for employees working in environments with controlled temperatures.

According to information from Pret's reporting system, there were several instances over the last 19 months where it needed to address problems with broken or frozen push buttons. One incident in January 2020 in the same kitchen involved a worker getting trapped in the walk-in freezer because they couldn't open the door from the inside.

On that occasion, the internal door release mechanism wasn't functioning properly.

Consequently, the sandwich chain pleaded guilty at Westminster Magistrates Court on Tuesday to an offence that contradicted the Health and Safety at Work Act 1974 after an investigation by Westminster Council.

Councillor Aicha Less, deputy leader and cabinet member for communities, public protection and licensing said: "The shocking details of this case show a lapse of due care and attention.

"This incident shows that overlooking basic safety measures can have the most serious consequences."

She added: "We hope the significant fine awarded in court acts as a warning, preventing this from ever happening again.

"Westminster City Council will continue to work with businesses to make sure the highest levels of health and safety are consistently maintained and educate staff in safe practice."

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A Pret A Manger spokesperson said: "We are incredibly sorry for our colleague's experience and understand how distressing this must have been.

"We have carried out a full review and have worked with the manufacturer to develop a solution to stop this from happening again.

"Following the incident, we have revisited all our existing systems and where appropriate, enhanced these processes, and have co-operated fully with Westminster City Council's investigation."