Bank customer left trapped for hours after glitch

A technical glitch at a U.K. bank left a man trapped on Sunday morning, after he had tried to withdraw cash from an ATM.

The customer was left stranded in a vestibule at a branch of Metro Bank for nearly three hours when the doors locked and he wasn't able to exit the building.

The man entered the bank - located about 18 miles west of the capital in the town of Uxbridge - at precisely 6:58 a.m. London time Sunday morning and was released at 9:49 a.m. by an engineer working on behalf of Metro Bank.

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Sana Khan, a passer-by who works at a nearby coffee shop, told the U.K. Mirror newspaper that he found the man waving frantically when he found out that he was locked in.

"He tried the handle of the door but it just wouldn't open," he said. "He slid his card through a small gap between the doors but when I tried it, the door still wouldn't open."

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Simon Dawson | Bloomberg | Getty Images

"I chatted to him and he seemed perfectly calm and relaxed and, when Metro Bank's customer service department opened, I rang them and told them of the problem," he added.

A spokesperson for the lender told CNBC that it was extremely sorry for the inconvenience caused and was currently investigating the cause of the problem. The man had decided to remain anonymous but Metro Bank had tried to contact him to discuss the glitch and issue an apology.

The new high street bank began life in 2010 and was founded by American Vernon Hill who originally found success with Commerce Bank in the 1970s. Metro Bank prides itself on its customer-focused strategy and calls itself a "banking revolution" at a time when its peers are being closely investigated by financial watchdogs.

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It now has 30 branches across Greater London and is open seven days a week, 362 days a year, with customers also being allowed to access ATM vestibules during night hours.

Sunday's incident echoes a similar ordeal experienced by a Texan tourist, back in October, who was accidentally locked inside a Waterstones book store in Trafalgar Square, London. The man had been left inside the store after spending "15 minutes" in the toilets and his plight managed to catch the attention of thousands of people on Twitter.