Banking giant Barclays has been fined £72 million by the City watchdog for failing to handle potential financial crime risks relating to a £1.88 billion transaction for ultra high-net-worth clients.
The Financial Conduct Authority (FCA) said the clients were "politically exposed persons" and should have been subject to extra checks and monitoring.
The FCA found Barclays used a lower level of due diligence and did not follow standard policies, and accused the bank of seeking to take on the clients as quickly as possible to make £52.3 million in revenues and of keeping the deal confidential.
The fine is the largest levied by UK regulators for financial crime failings.
While the FCA said the deal did not involve any financial crime, the nature of the transaction and people involved should have flagged up the need for extra checks within Barclays.
It added that the bank went to "unacceptable lengths to accommodate the clients", failing to ask for key information as it "did not wish to inconvenience" them.
Barclays agreed keep details of the transaction under wraps even within the firm, agreeing to a clause that would see the clients paid £37.7 million if they failed to comply with the confidentiality agreement.
The bank did not keep records of its due diligence relating to the transaction on any of its systems, instead keeping only hard copies, with few people aware of their existence or location, according to the FCA.
It added this meant Barclays was unable to respond to the FCA's request for information promptly.
The fine levied on the bank comprises the £52.3 million it made from handling the transaction as well as an additional £19.8 million penalty.