Royal Bank of Scotland and Barclays are among five banks handed a €1.07 billion (£930 million) fine for taking part in a foreign exchange spot-trading cartel, the European Commission has announced.
Citigroup, JP Morgan and MUFG were also fined by the EU antitrust group in two settlements.
Barclays, RBS, JPMorgan and Citigroup were hit with a combined fine of €811.2m in the first settlement.
The second settlement saw a €257.7m fine slapped on Barclays, RBS and MUFG Bank (formerly Bank of Tokyo-Mitsubishi).
The commission said the banks colluded on trading strategies to rig the spot foreign exchange market for 11 currencies.
Swiss bank UBS was involved but not fined after it alerted the EC about the two cartels.
The investigation revealed that some individual traders in charge of foreign exchange spot trading for currencies on behalf of their associated banks exchanged sensitive information and trading plans.
It also said the traders occasionally co-ordinated trading strategies through online chatrooms.
Most of the traders involved in the chatrooms knew each other on a personal basis, with one chatroom called “Essex Express ‘n the Jimmy”, as all the traders except one lived in Essex and met on a train to London.
The first infringement ran from December 2007 to January 2013, while the second ran from December 2009 to July 2012, the commission said.
Commissioner Margrethe Vestager said: “Companies and people depend on banks to exchange money to carry out transactions in foreign countries.
“Today we have fined Barclays, the Royal Bank of Scotland, Citigroup, JPMorgan and MUFG Bank and these cartel decisions send a clear message that the commission will not tolerate collusive behaviour in any sector of the financial markets.
“The behaviour of these banks undermined the integrity of the sector at the expense of the European economy and consumers.”