Citigroup has snatched back its position as the world's biggest currencies-dealing bank after a 12-year hiatus, taking the crown from Deutsche Bank, according to a closely followed industry survey.

The win is bittersweet; Citi regains the coveted market-leading position it once held for more than two decades, but it comes in a year when dozens of traders from banks across the market, including Citi, have been suspended or fired amid a sprawling probe into trading practices.