British bank NatWest on Thursday pleaded guilty to failing to prevent the laundering of nearly $500 million and could now face a similar fine.
The plea followed the first criminal prosecution of a financial institution under UK anti-money laundering laws.
The lender admitted three counts of failing to properly monitor the cash which was deposited in a customer's account between 2013 and 2016.
The Financial Conduct Authority regulator said NatWest had failed to adhere to anti-money laundering legislation in relation to an account held by jeweller Fowler Oldfield Ltd in Bradford, northern England.
The century-old jewellery firm was shut down following a police raid in 2016.
FCA prosecutor Clare Montgomery QC told Westminster magistrates court in central London that Fowler Oldfield's annual turnover was far higher than expected.
"The turnover of Fowler Oldfield was predicted to be £15 million per annum," Montgomery told the court.
"It was agreed that the bank would not handle cash deposits.
"However, it deposited £365 million ($496 million, 429 million euros), with around £264 million in cash."
At once stage, Fowler Oldfield deposited up to £1.8 million per day, she added.
The lender, formerly known as the Royal Bank of Scotland, could now face a fine of up to £340 million, according to media reports.
NatWest Chief Executive Alison Rose expressed "deep regret" over its conduct, adding the group has since ramped up its efforts to combat crime.
"We deeply regret that NatWest failed to adequately monitor and therefore prevent money laundering by one of our customers between 2012 and 2016," Rose said.
"In the years since this case, we have invested significant resources and continue to enhance our efforts to effectively combat financial crime."
Southwark Crown Court in south London will determine the size of the punishment at a hearing expected in the next four to eight weeks.
NatWest, which changed its name last year, remains majority-owned by the UK government after the world's biggest banking bailout amid the 2008 global financial crisis.
The bank cooperated fully with the FCA and no individuals have been charged under the proceedings.