The Financial Conduct Authority (FCA) has fined Barclays £26m for gold price fixing.
The fine relates to June 2012, when Barclays trader Daniel Plunkett exploited a weakness in the bank's systems and controls to influence the daily gold fixing, a mechanism introduced in 2004 to enable customers to buy gold at a single fixed price.
As a result of his actions, Barclays was not obligated to make a $3.9m payment to its customer, although it later compensated the customer in full. Plunkett's actions boosted his own trading book by $1.75m.
The FCA has fined Plunkett £95,600 and banned him from performing any function in relation to any regulated activity.
Tracey McDermott, FCA director of enforcement and financial crime, said: "A firm's lack of controls and a trader's disregard for a customer's interests have allowed the financial services industry's reputation to be sullied again.
"Plunkett has paid a heavy price for putting his own interests above the integrity of the market and Barclays' customer.
"Traders who might be tempted to exploit their clients for a quick buck should be in no doubt - such behaviour will cost you your reputation and your livelihood."
McDermott added the FCA is insisting other banks investigate their own reference rate and benchmark operations.
