U.S. bank Citigroup has been fined more than 61.6 million pounds ($78.5 million) for failures in its trading systems and controls in the United Kingdom, banking and financial regulators said on Wednesday.

The fine is one of the largest for controls breaches in the U.K. since the global financial crisis in 2008-2009.

The Prudential Regulation Authority (PRA) said in a statement that problems at Citigroup Global Markets Limited (CGML) had "crystallized into trading incidents," including one in May 2022 when an "experienced trader incorrectly inputted an order" that led to $1.4 billion being executed on European exchanges by mistake.

"Deficiencies in CGML’s trading controls contributed to this incident, in particular the absence of certain preventative hard blocks and the inappropriate calibration of other controls," the PRA said.

Citi had received "repeated supervisory communication" from the PRA to improve, but weaknesses persisted, the regulator said.

The PRA said it had fined Citi 33.88 million pounds for failings in its trading systems and controls between April 1, 2018, and May 31, 2022. That fine had been reduced by 30% after Citi agreed to resolve the issue.

The Financial Regulation Authority, in the same statement, said it fined Citi 27.76 million pounds after an investigation into similar matters.

"Firms involved in trading must have effective controls in place in order to manage the risks involved," said Sam Woods, CEO of the PRA and the Bank of England's (BoE) deputy governor for prudential regulation. "CGML failed to meet the standards we expect in this area, resulting in today’s fine."

Citi spokesperson Victoria Durman said the bank was "pleased to resolve this matter from more than two years ago, which arose from an individual error that was identified and corrected within minutes."

"We immediately took steps to strengthen our systems and controls, and remain committed to ensuring full regulatory compliance," she said via email.