Six banks have been collectively fined £2.6bn by UK and US regulators over their traders' attempted manipulation of foreign exchange rates.
HSBC, Royal Bank of Scotland, Swiss bank UBS and US banks JP Morgan Chase, Citibank and Bank of America have all been fined.
A separate probe into Barclays is continuing.
The fines were issued by the UK's Financial Conduct Authority (FCA) and two US regulators.
The country's Commodity Futures Trading Commission (CFTC) issued fines of $1.4bn to five banks, while the Office of the Comptroller of the Currency (OCC) added $950m in further fines to three lenders.
Separately, the Swiss regulator, FINMA, has penalised UBS 134m Swiss francs.
Barclays, which had been expected to announce a similar deal to the other banks, said it would not be settling at this time.
"After discussions with other regulators and authorities, we have concluded that it is in the interests of the company to seek a more general coordinated settlement," it said in a statement.
FCA boss Martin Wheatley told the BBC: "This isn't the end of the story."
"The individuals themselves will face the consequences," he said.
Several senior traders at the banks have already been put on leave and the Serious Fraud Office is in the process of preparing potential criminal charges against those alleged to have masterminded the scheme.
Failings 'undermine confidence'
The fines follow a 13-month investigation by regulators into claims that the foreign exchange market - in which banks and other financial firms buy and sell currencies between one another - was being rigged.
The massive market, in which $5.3 trillion worth of currencies are traded daily, dwarfs the stock and bond markets.
About 40% of the world's dealing is estimated to go through trading rooms in London.
There is no physical forex marketplace and nearly all trading takes place on electronic systems operated by the big banks and other providers.
Daily "spot benchmarks" known as "fixes" are used by a wide range of financial and non-financial firms to, for example help value assets or manage currency risk.
The FCA fined the five banks a total of £1.1bn, the largest fine imposed by it or its predecessor, the Financial Services Authority.
"At the heart of today's action is our finding that the failings at these banks undermine confidence in the UK financial system and put its integrity at risk," the FCA said.
The US regulator, the Commodity Futures Trading Commission (CFTC), has fined the same banks a total of more than $1.4bn (£900m).
"The setting of a benchmark rate is not simply another opportunity for banks to earn a profit. Countless individuals and companies around the world rely on these rates to settle financial contracts," said the CFTC's director of enforcement Aitan Goelman.
Another US regulator, the Office of the Comptroller of the Currency (OCC), fined Citibank, JP Morgan Chase and Bank of America a further $950m (£600m).
All three regulators found the attempted manipulation of the foreign exchange market had been going on for several years, with the FCA saying the failings occurred between 1 January 2008 and 15 October 2013. The CFTC said its investigation found the traders' misconduct took place between 2009 and 2012.
They found certain foreign exchange traders at the banks had coordinated their trading with one another to attempt to manipulate benchmark foreign exchange rates.
The CFTC said traders had used private online chat rooms to communicate. They had disclosed confidential customer order information and trading positions, and altered their positions accordingly to "benefit the interests of the collective group".
The FCA said the "tight knit groups" formed by traders at the different banks had described themselves as "the 3 musketeers", "the A-team" and "1 team, 1 dream".
It said traders had attempted to manipulate the relevant currency rate in the market, for example to ensure that the rate at which the bank had agreed to sell a particular currency to its clients was higher than the average rate it had bought the currency. "If successful, the bank would profit," the FCA added.
CFTC example of private chat room conversation:
Bank R Trader: 4:00:35 pm: well done gents
Bank W Trader 1: 4:01:56 pm: hooray nice team work
Bank U Trader: 4:02:22 pm: nice one mate
Bank V Trader: 4:00:51 pm: have that my son
Bank V Trader: 4:00:52 pm: hahga
Bank V Trader: 4:00:56 pm: v nice mate
Bank U Trader: 4:04:53 pm: that worked nice mate
Bank V Trader: 4:05:44 p.m.: big time mate.
The banks all issued statements following the fines:
- The Royal Bank of Scotland said it had placed six individuals into a disciplinary process and suspended three of them pending its own further investigation. Chief executive Ross McEwan said the bank had fallen "well short" of the standards he expected.
- HSBC said it "does not tolerate improper conduct and will take whatever action is appropriate".
- UBS said it had taken "appropriate disciplinary action" against employees involved in the matter.
- JP Morgan said the trader conduct described in the settlements was "unacceptable". It added it had made "significant improvements" to its systems and controls
- Citigroup said it had "acted quickly" once it became aware of the issues. "We have already made changes to our systems, controls and monitoring processes," it added.
Chancellor George Osborne said the fines "would be used for the wider public good".
"Today we take tough action to clean up corruption by a few so that we have a financial system that works for everyone. It's part of a long-term plan that is fixing what went wrong in Britain's banks and our economy," he added.
However, Professor Mark Taylor, a former foreign exchange trader and now dean at Warwick Business School, said the fines were "relatively small beer for banks that regularly report billions of dollars in annual profit".
"The interesting thing is that there are no individuals named as yet, and no individual prosecutions. This is still a possibility and it will be interesting to see how that pans out. At the moment, it's really only the shareholders - which in the case of RBS means British taxpayers - who suffer from these fines," he added.
For the opposition, shadow chancellor Ed Balls described the affair as "yet another shocking scandal involving the banks and underlines the need for fundamental reform and cultural change".
"This report shows that reform of our banks has a long way to go. We need reforms to pay and bonuses, with more transparency, greater clawback and a tax on bank bonuses," he added.
Bank of England cleared
Separately, the Bank of England - which had been accused of knowing about the foreign exchange scandal, but doing nothing about it - published a separate report by Lord Grabiner, clearing its officials.
"There was no evidence that any Bank of England official was involved in any unlawful or improper behaviour in the FX [foreign exchange] market," it said.
It said the suspension of the Bank's chief dealer in March, and his subsequent dismissal on 11 November was unrelated to the foreign exchange scandal.
"The individual's dismissal was as a result of information that came to light during the course of the Bank's initial internal review into allegations relating to the FX market and Bank staff. This information related to the Bank's internal policies, not to FX," a Bank spokesperson said.