Dutch lender Rabobank has been fined 774 million euros (£663 million) by UK and overseas regulators as it became the fifth group to reach a settlement over the Libor rate-rigging scandal.
The group's penalty includes a £105 million fine imposed by Britain's Financial Conduct Authority (FCA) for "serious, prolonged and widespread misconduct" relating to interbank lending rates, while it has also agreed penalties with regulators in the Netherlands, United States and Japan.
Rabobank chairman Piet Moerland resigned immediately and apologised for the "inappropriate conduct" of around 30 employees found to be involved in attempting to fix interbank lending rates.
He said he was "shocked" by their behaviour and added the bank also failed to "sufficiently appreciate" the risks of Libor and Euribor submitting processes.
The FCA's fine is the third biggest ever imposed by the regulator and its second highest for Libor manipulation.
It found more than 500 attempts within Rabobank to manipulate Libor, with the group's London office significantly involved in the scandal, alongside offices in Utrecht, the US, Japan, Singapore and Hong Kong.
Rabobank employs up to 200 front office staff in its London office, including money market traders.
The FCA said Rabobank's misconduct was "among the most serious" uncovered so far by the regulator in relation to Libor.
It found emails and communication revealing hundreds of requests to manipulate the rate, which governs the price of hundreds of trillions of pounds of loans and transactions around the world, including household mortgages.
In one example, a Rabobank manager said to another trader who had made requests to Libor submitters that he was "fast turning into (that trader's) bitch!!!!".
Another Libor submitter said to a trader that he would "never change libors without consulting you", adding "we are on the same team".
Tracey McDermott, the FCA's director of enforcement and financial crime, said: "Traders and submitters treated Libor submissions as a potential way to make money, with no regard for the integrity of the market. This is unacceptable.
"Rabobank's flawed assurances and failure to get a grip on what was going on in its business were extremely disappointing."
Rabobank's fine comes just a month after City broker ICAP was hit with a £54 million penalty by US and UK regulators, following a £290 million fine for Barclays, £940 million for Swiss bank UBS, and £391 million for the Royal Bank of Scotland.
The FCA said the level of its fine reflected the widespread and blatant attempts to manipulate Libor, as well as the group's failure to address its management and control of rate-setting processes.
It said the practice of attempts to fix the rate was conducted in open conversations, chat forums and group emails.
The FCA added that Rabobank did not get its Libor processes up to scratch until nearly a year and a half after assuring the regulator it was fit for purpose.
It also failed to act on information given by a Libor submitter in 2009 that flagged up attempts at rate manipulation, according to the FCA.
Mr Moerland, who has been replaced on an interim basis by executive Rinus Minderhoud, said: "I sincerely regret that a number of Rabobank employees acted in an inappropriate manner. This should never have taken place at Rabobank.
"The conduct of these individuals, and the language of some of the individuals' communications, has shocked me."
Rabobank said that employees involved in serious misconduct have been sacked, with other disciplinary action including formal warnings, financial sanctions, and the removal of managerial responsibilities.
It has clawed back 4.2 million euros (3.6 million) of staff bonuses for the period between 2009 and 2012, while it said senior executives had forfeited two million euros (£1.7 million) of pay.
Alongside the FCA fine, Rabobank has agreed to pay 475 million dollars (£296 million) to America's Commodity Futures Trading Commission (CFTC), 325 million dollars (£202 million) to the US Department of Justice, and around 96 million dollars (£60 million) to the Dutch Public Prosecution Service.