British authorities have launched a criminal probe into allegations of price rigging in foreign exchange markets, the Serious Fraud Office said.
"The director of the Serious Fraud Office has today opened a criminal investigation into allegations of fraudulent conduct in the foreign exchange market," it said in a statement.
No further details were given in the statement.
EU, British, and US and other regulators have levied huge fines on some of the world's biggest banks and investment houses for manipulating currency markets worth trillions of dollars.
In June Britain's government, the Bank of England and financial regulators proposed legislation to punish foreign exchange rigging with criminal sanctions.
The legislation was an extension of new laws regulating the inter-bank Libor benchmark interest rate.
Some traders have been found guilty of manipulating the Libor and Britain has already threatened prison for those found guilty of rigging it.
The Serious Fraud Office had previously said that it was looking at "complex" evidence before deciding whether to launch an inquiry.
Barclays, HSBC and Royal Bank of Scotland have all confirmed that they are part of the ongoing forex market investigations.
Deutsche Bank, Swiss lender UBS and US pair Citi and JPMorgan Chase have also revealed that they are co-operating with regulators over the affair.